There is nothing new about a woman and her lover killing her husband. That’s been going on since Clytemnestra and Aegisthus murdered Agamemnon. What inspired James M. Cain to write Double Indemnity was the additional feature of insurance, as in the case of Ruth Snyder, whose murder trial Cain covered as a journalist in 1927. While having an affair with Judd Gray, she got her husband Albert to take out a life insurance policy with a double indemnity clause, one that promised to pay extra in case the insured died by accident or by some violent means. This added a whole new dimension to an old story.
Let this be a warning to all husbands. The whole point of life insurance is to provide for your loved ones, say your wife and children, in the event of your death. The manner of your death has nothing to do with their dependency on you as a breadwinner. Their needs will be the same whether you die in your sleep or fall off a cliff. So, if your wife seems to be taking an undue interest in the double indemnity clause of the policy you are considering, this should occasion a moment of reflection.
My mother once told me that a man might be averse to taking out a life insurance policy for fear that after his death, his wife will squander all the money on some younger man. But if the policy also has a double indemnity clause that the wife keeps asking the salesman about, she may already have that younger man, with special plans for him later. Some believe Albert refused to take out that policy, for just that reason, but with the connivance of the insurance salesman, anxious to get his commission, Albert’s name on the policy was forged.
Killing Albert turned out to be something of a challenge, but after several attempts, Snyder and Gray managed it. They were sloppy, however, leaving behind incriminating evidence. Eventually, they turned on each other, as if that would help. Both of them died in the electric chair.
Never mentioned in the story of Ruth Snyder is that, in all likelihood, there was a time when she and Albert loved each other very much. They took their vows in all sincerity, fully believing every word of the ceremony, “to have and to hold from this day forward, for better or for worse, for richer, for poorer, in sickness and in health, to love and to cherish; from this day forward until death do us part.” That last part turned out to have a significance neither of them could have imagined at the time.
One of the painful things about the movie Two for the Road (1967) is the way it keeps jumping back and forth between the four stages of love: when the man and woman first meet, their courtship, their marriage, and the affairs they have after love has died. The movie won’t let us forget how these two miserable people were once so much in love. But in real life, we do forget. And so it was, in all probability, that while Ruth and Judd were cuddling in bed, they convinced themselves that she never felt that way about Albert, and Judd never felt that way about his wife. More importantly, it never occurred to them that the contempt, if not hatred, they presently had for the ones they married, they might someday have for each other.
Have there been stories in which men have murdered their wives for the insurance money? Yes, of course. But such stories just do not capture the imagination in the same way. Perhaps it’s because men are more violent than women, more likely to commit murder, so we are not as shocked when a man murders his wife. I regularly hear about men killing their wives or girlfriends and whoever else happens to be in the room on the nightly news. And that’s the local news I’m talking about. As for women, perhaps it’s because we tend to be sentimental about women, seeing them as being more caring, loving, and nurturing than men are, and so it is more shocking when a woman murders her husband. Still, there have been movies made in which a man murders his wife for money, such as Sorry, Wrong Number (1948), but they just don’t horrify us as much as when it is the woman that murders her husband.
Just as there is nothing new about a woman murdering her husband, neither is there anything new about murder being committed for money. But when it is money being paid out by an insurance company, money also becomes a motive for solving the crime. Cain also made an insurance policy part of the plot in the The Postman Always Rings Twice, which was made into a movie in 1946. Normally, if the beneficiary of a policy is charged with murdering the policyholder, the insurance company will delay paying the claim: if the beneficiary is acquitted, the company will pay; if he is convicted, it will not. In this movie, however, it is the other way around. The prosecutor waits to see what the insurance company’s investigators come up with. When these top-notch investigators fail to find incriminating evidence, the insurance company pays the claim. That is when the prosecutor realizes he doesn’t have a case. I don’t think that’s the way things work in real life, but the idea is that a police detective gets paid whether he solves a crime or not, but when an insurance company stands to lose a lot of money, they will try much harder to prove foul play.
As another example, an insurance investigator solves a crime in The Killers (1946) because his company had to pay off when the money stolen was never recovered. In a similar way, money is also the motive in films noir in which a private detective solves a crime when the police failed to. So, instead of the police solving the crime as part of their duty to enforce the law, films noir cynically reject this idealistic notion by making money the central motive of the investigation rather than justice.
In the case of Snyder and Gray, the police solved the crime all by themselves. The insurance policy merely supplied the motive. But in his novel, Cain wisely made Keyes, Claims Manager for General Fidelity of California, the principal detective on the case. Keyes seems to have uncanny powers of intuition when it comes to spotting insurance fraud. In the movie, he refers to it as the “little man” inside his chest, who gives him indigestion whenever a phony claim comes before him. But it is an intuition distilled from years of having immersed himself in statistics and actuarial tables, along with dealing with insurance fraud directly. In the movie, there is a scene in which Keyes (Edward G. Robinson) is talking to Walter Neff (Fred MacMurray), the insurance salesman who conspired with Phyllis Dietrichson (Barbara Stanwyck) to murder her husband and make it look like an accident. With disgust, Keyes says the inquest was over with in forty-five minutes. “Verdict, accidental death.” Neff asks what the police figure. Keyes replies: “That he got tangled up in his crutches and fell off the train. They’re satisfied. It’s not their dough.”
In the novel, Walter gets Phyllis to show up at the inquest with a minister. “Once a coroner’s jury sees that it’s a question of burial in consecrated ground,” Walter informs the reader, “the guy could take poison, cut his throat, and jump off the end of a dock, and they would still give a verdict, ‘in a manner unknown to this jury.’”
There was another improvement made by Cain over the case of Ruth Snyder. She had her husband take out a life insurance policy with an extra payout for accidental death. Cain made the policy one of accident insurance by itself. Happening to be in the neighborhood, Walter Huff (“Neff” in the movie) decides to stop by the house of one of his customers, Mr. Nirdlinger (“Dietrichson” in the movie), in hopes of getting him to renew his automobile insurance. As it is the middle of the day, he has little hope of finding him at home, but decides it’s worth a try.
Once he gets past the maid, he finds himself talking to Mrs. Nirdlinger. She tells him her husband is thinking about switching to the Automobile Club. After a while, Huff begins to suspect she wants him to split the commission with her in exchange for getting her husband to renew with General Fidelity of California. Huff informs the reader that there is a lot of that going on, but it wasn’t the sort of thing a reputable insurance agent like himself would participate in. But while those thoughts are going through his head, he finds himself appreciating her figure beneath her blue pajamas. He is wondering if his ethical standards would be able to resist splitting a commission with an attractive woman like Mrs. Nirdlinger.
“But all of a sudden she looked at me, and I felt a chill creep straight up my back and into the roots of my hair. ‘Do you handle accident insurance?’”
Huff informs the reader that accident insurance is sold, not bought, so her asking about it out of the blue is most unusual. In addition to that, the payout is substantial, for which reason it lends itself to insurance fraud. Finally, unlike life insurance, no physical examination is required, and the insured doesn’t even have to know anything about it. All the insurance company wants is the money for the premium, and “there’s many a man walking around today that’s worth more to his loved ones dead than alive, only he don’t know it yet.”
Another improvement made by Cain over the Snyder case is that of having the wife’s lover be the insurance salesman, someone that knows what a claims adjuster will look for, and knows where people committing insurance fraud tend to slip up. There is a scene in both the book and the movie in which Keyes is upset about a policy that Walter sold on a truck that later became the basis for a fraudulent claim. Walter points out that he had attached a memo saying the man should be investigated first. This lets us know that Walter is also alert to the possibility of fraud, which is why Keyes later tries to talk him into becoming his assistant. And so, whereas Snyder and Gray committed a clumsy murder that even an ordinary flatfoot could see through, the novel becomes a game of wits between two men, each an expert in the insurance business, making it a story in which one of them sets out to commit the perfect crime that will escape the detection of the other.
Cain’s novel is in the form of a first-person narrative, in which Walter tells us how he became involved in a scheme to murder a man’s wife. In this way, we are privy to his thoughts, such as his suspicion that Mrs. Nirdlinger wanted a cut of the commission, his forebodings about her interest in accident insurance, and his commentary on the sinister aspect of such insurance. And, like most such novels, it is told in the past tense. Movies, on the other hand, are usually in the present tense, and we merely watch events unfold. Only through dialogue do we get any insight into what someone is thinking. Therefore, in order to better represent such a novel as a movie, it should be told in flashback, which is what is done here.
The flashback, however, is not simply a way of making a movie unfold like a first-person narrative in a novel, for the flashback form also gives us some idea how things will end up. And so it is that whereas in the novel, the story begins with Walter telling us why he happened to show up at the Nirdlinger house in the middle of the day, in which case we haven’t the slightest idea that anything bad is going to happen to him, the movie lets us know right off that something bad did happen, and Walter’s narration will explain what led up to it. Just as Cain made improvements over the Snyder case in writing his novel, the movie makes improvements over the novel, and this flashback device is one of them.
During the credits, while we hear ominous music, we see the silhouette of a man moving toward us with the aid of two crutches. We sense that he is dangerous, but this is contradicted by the crutches, for how could a man in his condition, we wonder, be dangerous? As the credits end, we see a city street late at night. A car going fast almost crashes into some men doing repairs underneath a sign that says, “Los Angeles Railway Maintenance,” foreshadowing the role that a train will have in this story. The car swerves and continues to speed recklessly along the streets, though no one is in pursuit. Finally, it pulls up in front of a building. A man gets out with a coat draped over him. It looks like the same man that was in silhouette. The elevator operator lets us know that the man is Walter Neff. He lets him out on the twelfth floor, which is the main office of Pacific All Risk Insurance Company.
When he gets to his office and removes his overcoat, we see that he has been shot, a small spot of blood near his left shoulder, incapacitating his left arm, much in the way that the man in silhouette had an incapacitated left foot. He removes his fedora, and with a little difficulty, uses his thumbnail to ignite a match so he can light up a cigarette. Once he takes a drag and exhales, he is ready. He puts a new cylinder in the Dictaphone, addressing an office memorandum to Barton Keyes, Claims Manager. He remarks that what he is about to say may sound like a confession, but he doesn’t like that word. He says he just wants to set him straight on the Dietrichson claim.
In other words, he’s not worried about his wound, and he’s not worried that he is about to incriminate himself in a couple of murders. He tried to pull off the perfect crime, and almost did so, fooling even Keyes, the one man he most feared would see through his scheme. It is important to him to let Keyes know how it all went down, where Keyes went wrong, and why. He then begins where the novel did, with his decision to stop by the Dietrichson house, which he says must have cost somebody $30,000, if he ever finished paying for it. (The year is 1938, so that would be well over $500,000, adjusted for inflation, in today’s dollars.)
Another improvement in the movie over the novel is due to the fact that Billy Wilder, the director, got Raymond Chandler, author of novels like Farewell, My Lovely and The Big Sleep, to help with the screenplay. And so, whereas there is something a little hurried and abrupt about Cain’s style of writing, Chandler, who said he never cared for Cain’s novels, was able to smooth out the story and give it some style. For example, when Walter Neff arrives at the Dietrichson house for the first time, he notes the smell of honeysuckle in the air, leading him to ask, “How could I have known that murder can sometimes smell like honeysuckle?”
What I like about that line is the way it introduces another element in the crime beyond motive. Early in his confession on the Dictaphone, Neff admits to committing murder, saying he killed Mr. Dietrichson for money and for a woman. But it’s not merely that sex was a motive for the crime, along with the money. Rather, it’s the effect sex had on his attitude about murder that is important. Sex has a way of soothing our conscience, keeping us from having the feelings of guilt that we should. Usually, this just makes it easier to violate some sexual taboo. But it can also make it easier to do something evil that is not sexual in nature. A man and woman in love can sometimes talk themselves into committing a crime they would never dream of doing otherwise. The crime becomes an expression of their love for each other. It’s so sweet that they would even kill for each other. Hence the remark about honeysuckle.
In the beginning, Phyllis tries to get Walter to allow her to get accident insurance on her husband without his knowing about it. She hates her husband, but has no definite plan to murder him. She is just hoping that once she gets the policy, her husband will have an accident in the oil fields and die. We later find out from her stepdaughter Lola that Phyllis may have contributed to her mother’s death while acting as her nurse during an illness. According to Lola, while her mother had a fever, Lola walked into the bedroom and found that Phyllis had the windows wide open, letting in the cold winter air. After the mother died, Phyllis then married Lola’s father. This kind of opportunism is probably what Phyllis had in mind for her husband once she got him the accident policy: wait for propitious circumstances, and then help them along a little. Making Phyllis a nurse was another improvement on Cain’s part over the Snyder case. It reinforces those sentimental feelings we have about women, alluded to above, about caring and nurturing, all the better to unnerve us when she turns out to be coldblooded.
Limiting Phyllis’s dark past to what she did with Lola’s mother in the movie is a major improvement over the novel, where it turns out the Phyllis is a serial killer from way back. As a pulmonary nurse, before killing the first Mrs. Nirdlinger, she had already killed three children, making it appear they died of pneumonia. She did this because she was related to one of them and, as executrix, was able to take possession of the property herself. The other two children were killed just to keep the police from focusing on the one she made money off of. Then it turns out there were five mysterious deaths before that, two of which Phyllis profited from. And Lola will be next, so that Phyllis can get whatever she has as well.
But it gets worse. In the novel, Phyllis says she doesn’t hate her husband. As she agrees to go along with the plan to murder him, she says, “I haven’t any reason. He treats me as well as a man can treat a woman. I don’t love him, but he’s never done anything to me.”
Then comes a strange justification. She says, “He’s not happy. He’ll be better off—dead.” In a sense, she knows it’s not true, but she says it’s based on a strange notion she has:
“I know it’s not true. I tell myself it’s not true. But there’s something in me, I don’t know what. Maybe I’m crazy. But there’s something in me that loves Death. I think of myself as Death, sometimes. In a scarlet shroud, floating through the night. I’m so beautiful, then. And sad. And hungry to make the whole world happy, by taking them out where I am, into the night, away from all trouble, all unhappiness… Walter, this is the awful part. I know this is terrible. I tell myself it’s terrible. But to me, it doesn’t seem terrible. It seems as though I’m doing something—that’s really best for him, if he only knew it. Do you understand me, Walter?”
Later in the movie, Lola says that before her father died, she saw Phyllis trying on a black hat, pinning on a veil, as if preparing for how she will look in mourning. But Lola sees more than that in the novel. She tells Walter she plans to go to the police and tell them what she knows:
“I’ll tell them everything they need to know. I told you there was plenty more, besides what I told you. I’ll tell them to ask her about the time I came in on her, in her bedroom, with some kind of foolish red silk thing on her, that looked like a shroud or something, with her face all smeared up with white powder and red lipstick, with a dagger in her hand, making faces at herself in front of a mirror….”
At the end of the novel, after Phyllis and Walter try to kill each other, Keyes doesn’t want the bad publicity of a trial, so he just puts them on a ship sailing south without either of them realizing the other one is on the ship too. When they meet each other, Phyllis suggests that they could be married, but not with any illusions about their having a future. But then she decides she has a different marriage in mind, saying the time has come “For me to meet my bridegroom. The only one I ever loved. One night I’ll drop off the stern of the ship. Then, little by little I’ll feel his icy fingers creeping into my heart.” Walter says he’ll give her away, meaning he will join her. There is a shark following the ship. They agree to wait until the moon is up so that they can see the dark fin of the shark when they dive into the water to meet their death. These are some of the last words Walter writes:
I’m writing this in the stateroom. It’s about half past nine. She’s in her stateroom getting ready. She’s made her face chalk white, with black circles under her eyes and red on her lips and cheeks. She’s got that red thing on. It’s awful-looking. It’s just one big square of red silk that she wraps around her, but it’s got no armholes, and her hands look like stumps underneath it when she moves them around. She looks like what came aboard the ship to shoot dice for souls in the Rime of the Ancient Mariner.
Instead of letting it be a story about a woman who has come to hate her husband and wants to kill him for the insurance money, as in the case of Ruth Snyder, Cain has turned the Phyllis of his novel into a fantastic monster. The movie wisely returns to the idea that Phyllis is just your ordinary psychopath, one that you or I might inadvertently find ourselves married to, and not some utterly deranged serial killer.
At first, all Walter was hoping for was to have an affair with Phyllis. But when he hears about her plan to get the accident policy on her husband without his knowing about it, Walter immediately realizes that she is dangerous, and he gets up and leaves, picking up his hat as he heads for the door. There follows a scene that many people miss, while others catch it, but think it is a goof. That night, as Walter broods over his situation with Phyllis, she shows up at his apartment. When he opens the door, she says, “You left your hat today.” A lot of people, including professional critics, think that Walter did leave his hat behind at her house. Others, having noticed that Walter picked up his hat on the way out the door, conclude that this is a mistake. However, it is obvious that Phyllis has no hat in her hand as she stands in the doorway.
What Phyllis is doing is amusing herself with the remark about the hat. If a man has recently met a woman and would like to see her some more, he may pretend to accidentally leave something behind at her home. We don’t wear hats so much any more, but an umbrella is a good substitute. Then the man can call her up the next day and say, “Did I leave my umbrella over at your place yesterday?” When she says that he did, he can then ask if it would be all right to drop by and pick it up. With a little luck, one thing will lead to another. Phyllis is alluding to that ruse by making believe she has his hat and is using it as an excuse to see him. In so doing, she is essentially saying, “We both know why I’m here.”
At least, we figure she is there to have sex with Walter. But during his confession on the Dictaphone, Walter says, “Yes, I killed him. I killed him for money and for a woman. And I didn’t get the money, and I didn’t get the woman. Pretty, isn’t it?” That remark, “I didn’t get the woman,” always puzzled me. Didn’t he get the woman when she came over to his apartment, once before the murder, with the hat routine, and again after the murder, when Walter says Keyes will be watching her, and they will have to quit seeing each other for a while? We’re all used to scenes fading out in old movies, where we are supposed to imagine the man and woman having sex, and there was a fade out at a critical moment in the second visit to his apartment. Well, I finally figured that he meant that while they did have sex once or twice, he still didn’t get the whole woman. But you never do. That’s why they call it a piece. In the novel, however, it is clear that they did not have sex on either night that she came over to his place or at any other time. All they did was plan the murder. I should think a man would want to have sex with a woman before agreeing to kill her husband, but I’m just an armchair philosopher, so what do I know?
On the night she and Walter trick her husband into signing the application for the accident insurance, Walter hears him say he is taking a trip to Palo Alto. Walter tells Phyllis to get him to take the train. He knows that getting killed while riding a train is so rare that the $50,000 policy will pay off at twice that amount owing to a double indemnity clause in the policy, which would be over $1,800,000 adjusted for inflation. In the novel, Walter plans on murdering her husband on a train right from the start, without the slightest idea of how to get him on a train. The movie is better in having the possibility of an accident on a train just fall into their laps.
In the novel, Phyllis tells Walter that her husband wants her to go with him to Palo Alto, saying, “He’ll raise an awful fuss if I don’t go.” Walter dismisses that problem:
“Yeah? Listen, don’t give yourself airs. I don’t care if it’s a class reunion or just down to the drugstore, a man would rather go alone than with a wife. He’s just being polite. You talk like you’re not interested in his class reunion, and he’ll be persuaded. He’ll be persuaded so easy you’ll be surprised.”
“Well, I like that,” she says. (The woman who’s planning on killing her husband is indignant that he doesn’t want her company.)
“You’re not supposed to like it,” Walter replies. “But you’ll find out.”
By chance, Mr. Dietrichson breaks his leg. That too turns out to be to their advantage. On the night of the murder, Walter hides in the backseat of the car that Phyllis will use to drive her husband to the train station. In the novel, Walter says, “Believe me it’s an awful thing to kibitz on a man and his wife, and hear what they really talk about.” Just another one of Cain’s disparaging remarks about marriage, based on his personal experience, no doubt.
They kill her husband before he gets on the train. In the novel, Walter says, “I took one of the crutches and hooked it under his chin. I won’t tell you what I did then.” I guess Cain felt it would be indelicate to go into details about the way he used the crutch to break the man’s neck.
Then Walter pretends to be the husband and boards the train, jumping off soon after, before the train can pick up much speed, after which they dump the husband’s body on the tracks. Because Neff put his own leg in a phony cast and got on the train with the crutches, people were confident they had seen Dietrichson get on the train. As Keyes says later, the witnesses had the crutches to look at, so they never really saw the man at all.
In the novel, after Walter gets back to his bungalow, the enormity of what he has done begins to overwhelm him:
I dived for the bathroom. I was sicker than I had ever been in my life. After that passed I fell into bed. It was a long time before I could turn out the light. I lay there staring into the dark. Every now and then I would have a chill or something and start to tremble. Then that passed and I lay there, like a dope. Then I started to think. I tried not to, but it would creep up on me. I knew then what I had done. I had killed a man. I had killed a man to get a woman. I had put myself in her power, so there was one person in the world that could point a finger at me, and I would have to die. I had done all that for her, and I never wanted to see her again as long as I lived.
That’s all it takes, one drop of fear, to curdle love into hate.
Eventually, Walter tells Phyllis that they will have to quit seeing each other for a while, until Keyes is through investigating. In the novel, he says, “That night I did something I hadn’t done in years. I prayed.” Perhaps the prayer went something like this: “Dear God, please don’t let Keyes find out that I killed Phyllis’s husband.”
All right, back to the movie. Suspecting that Mr. Dietrichson was murdered, Keyes realizes it would be easier to murder him before he got on the train, which is what happened, rather than kill him on the train. That means that Phyllis must have had a male accomplice pretend to be her husband. Keyes starts having her house watched. As a result, Walter and Phyllis have to stop seeing each other until the investigation is over. Phyllis’s stepdaughter, Lola, had a boyfriend, Nino Zachetti, but they broke up, and soon he and Phyllis start having an affair. Keyes concludes that Nino is the accomplice in the murder and calls off the surveillance. He tells Walter he is going to reject the claim, daring her to take it to court.
What follows from this point on seems to make no sense. Walter goes over to Phyllis’s house intending to kill her, and she slips a pistol under the cushion so that she can kill him. Let us consider the situation from Phyllis’s point of view. Unless we assume she is psychic, she does not know of Walter’s plans to kill her. So, what does she hope to gain by killing Walter? The police have already dropped the case, but if Walter is murdered, the police will not only investigate his death, but it might make them reconsider her husband’s death as well, since Walter supposedly sold him the policy. Furthermore, shooting Walter in her house will not only get blood all over the place, but she will then have to dispose of the body. What is she going to do, cut him up in the bathtub like the guy in Rear Window (1954), and then make several trips to the city dump with the body parts in a suitcase? The prudent thing for her to do is to just sue the insurance company. If she wins, she can give Walter his cut and all will be well. If she does suspect Walter wants to kill her, then she should simply refuse to let him come over to her house. After all, he is not going to gun her down on Main Street. Therefore, it makes no sense for her to shoot Walter.
Now let us look at it from Walter’s point of view. By this point, Walter has obviously given up on getting his share of the money, because she cannot very well collect and split with him after he kills her. So, what does he hope to gain by killing Phyllis? All Keyes knows is that Phyllis has been seeing Nino, which means she has been having an affair with a younger man. Big deal. Keyes says he has investigated Nino’s movements on the night of the murder, and they cannot be accounted for. We later find out from Lola that he broke a date with her the night of the murder, claiming he was home sick. But that is not exactly evidence that will convict a man of murder. In any event, we know that Nino did not do it, so he is not going to get tripped up in a cross examination in court, as Keyes seems to think. With nothing more to go on, Keyes has little chance of successfully denying Phyllis’s claim in court, and it certainly would not be enough for the police to reopen the case. Walter should just continue to stay away from Phyllis. Whether she wins her case, and if she does, whether she splits the money with him, there is no point in killing her. And there is always the chance that she might win and pay him off anyway.
But let us assume that beyond all reason, Walter is afraid that enough would come out in the civil suit that would lead the police to reopen the investigation into the death of Phyllis’s husband, and make them suspect not Nino, but Walter. In that case, Walter should simply turn in his resignation at the insurance company and go to Mexico for a while. If Phyllis’s lawsuit does not lead to a new police investigation in which he becomes a suspect, he can always return to the United States later; if it does lead to a new investigation, and he does become a suspect, he can continue to hide out in Mexico. But his killing her will definitely cause the police to investigate. Walter’s plan is that Nino will be blamed for Phyllis’s murder. But Nino might have an alibi for that night. As it turns out, Nino was coming to see Phyllis just as Walter was leaving the house, but Walter could not know Nino was going to do that. Walter tells Phyllis, just before he kills her, that he knows Nino will be coming to see her in fifteen minutes with the cops right behind him, because it has been all set up. Now, how would he know that? And set up for what? If they plan on arresting him, they should just go to his apartment. Furthermore, Nino would have no motive for murdering her. If anything, the police might end up suspecting Walter. Therefore, it makes no sense for Walter to kill Phyllis.
Since Nino was coming over to see Phyllis, that means that if she had successfully killed Walter, Nino would have walked in the house and seen Walter’s corpse lying on the middle of the living room floor. And then what? Will Phyllis ask him to help her dispose of the body of the man that helped her kill her husband? How likely is he to go along with that? He was fine having sex with Phyllis, but I doubt that he would want to get mixed up in a couple of murders.
However, it is reasonable to assume that two people who have committed a murder and are afraid of getting caught might not be thinking clearly. In fact, if they had been thinking clearly, they would never have committed that murder in the first place. It is especially hard to believe that a man could have an affair with a married woman, conspire to kill her husband, and not have it occur to him that one of these days she may turn on him too. And so, I suppose that if people are foolish enough to commit such a murder, they would be foolish enough to think that killing their partner in crime would solve their problems. So, their behavior makes sense on an emotional level.
You really have to give those hormones credit!