Sackett makes a personal wager (of $100) with Cora's weasely attorney Arthur Keats (Hume Cronyn), that Cora is a "gone goose."

In municipal court for the arraignment, The People vs. Cora Smith, Cora is shocked when she realizes that Frank has turned against her and betrayed her. Her lawyer has her plead 'guilty' to both counts: murder (against Nick Smith) and the attempted murder (of Frank Chambers).

In a courtroom interrogation room alone with Frank, Cora is incensed by Frank's accusation that she is solely to blame for Nick's death. The chemistry and love between the two starts to disintegrate and dissipate rapidly and they have their first showdown:

Frank: We've been double-crossed, Cora. That lawyer Keats, he's nothing but a police stool pigeon.
Cora: (incensed) I've been double-crossed, not you. Oh I see it all, now. I see why I had to drive the car, not you. And that other time, why it was me that had to do it and not you.
Frank: That's not so.
Cora: Oh yes it is. I used to think to myself the reason I fell for you was because you were smart. Now I find out that you are smart. Double-crossed, hah! I'll say I was. You and that Keats fixed it up so that I tried to kill you too. That was to get you clear. And then you two fixed it up to plead me guilty. Well, listen, Mr. Frank Chambers. When I get through, you'll find out there's such a thing as being too smart.

When her lawyer Keats enters the room, Cora de-masculinizes both Frank and her own lawyer. She vows to "make a statement" that confesses the real truth about what really happened:

(To Keats) So you, you and this man [Frank], this so-called man, you two framed me so that I would get it and he would go free. Well, he's not gonna squirm out of it that easy...He was in this mess as much as I was and I'm gonna tell it to the world....Oh, he's not gonna get away with it. He's not gonna get away with anything from now on because I'm gonna tell it all right now...You handled it before, now I'll handle it.

In the interrogation room, her statement is taken and typed by Keats' goon Ezra Liam Kennedy (Alan Reed) as she spitefully circles around Frank in a wheelchair and fully implicates Frank in the murder:

This will be a full and complete confession of how Frank Chambers and I deliberately planned and carried out the murder of my husband Nicholas Smith. Frank Chambers and I are equally guilty, although it was Frank who smashed Nick in the head before the car went over the cliff....

[Text seen only in the typed version: "We were in our right minds and the crime was premeditated and carefully worked out in all its details to make the death appear accidental. We even planned to have Frank Chambers injured to lend reality to our story of the supposed accident."]

That's all, except I didn't know anything about that ten-thousand dollar insurance policy. Anyway, we didn't do it for that reason at all.

After turning against Frank, Cora lights a cigarette for herself - and then with a touch of regret about their love affair and where it's headed, she shares her cigarette with Frank. Feeling defeated by the legal maneuverings of the district attorney, Keats tells them how they have both fallen for "Sackett's trump card":

Keats: Of course, you know the district attorney fooled you into that confession, don't ya? And you fell for it, both of ya. He planned to get you working against each other. Don't you see?
Cora: You bet I see. (To Frank) So when Sackett couldn't get anything out of me, he started in on you, and right away you turned yellow.
Keats: Yellow. Yellow's a color you figure on in a murder. And nobody figures it better than Kyle Sackett. That was Sackett's trump card. Once he tricked you [Frank] into signing that complaint against her, he knew no power on earth could keep you [Cora] from turning on him [Frank]. That way, he gets you both.
Cora: (to Keats) If you knew all that, why didn't you stop me from confessing?
Keats: Oh, I tried. I tried. But nobody could have stopped ya. However, now that you've got it off your chest...

Then, Keats turns the tables on them - he calls in Mr. Kennedy, the man who transcribed Cora's signed confession and asks him: "What did you do with it?" Kennedy responds: "I gave it to Jimmy White to lock up in your safe like you told me to." The transcriber is not from the DA's office, but Keats' own personal "gumshoe man." Keats is now able to keep Cora's full transcribed confession from being seen by the prosecutor. To excuse his equally-corrupt tactics, Keats nastily admits his own ruthless strategy to Cora - to have her privately vent her denunciatory anger at Frank instead of in the courtroom before the judge and prosecuting DA:

Keats: With the District Attorney using high pressure tactics, I had to fight fire with fire. Since you [Cora] were due to spill the beans anyway, I figured you'd better do it to my man rather than to Sackett's...That's why I said we'd plead guilty so as to stop everything cold in that courtroom before you blew your talker right there and then...
Frank: Then the District Attorney's got nothing against me.
Keats: Nope, Frank, you're not even under arrest.
Cora: Oh, sure. He goes free, and I get tossed in - for murder and attempt!
Keats: Unless, unless you let me handle it....Listen my girl, you're still in plenty of trouble because we don't know exactly what evidence Sackett's got against us. From now on, you speak only when you're spoken to. And in that court tomorrow, try and look as young and innocent as possible under the circumstances. And remember, I'm the only hope you've got.

In the California Superior Court, Cora's lawyer Keats then reverses her original "guilty" plea (for the murder of Nick Smith and the attempted murder of Frank) and contends that his client "protested her innocence from the beginning." Keats consults privately with Sackett and directs him how to proceed with the case, because he is lacking in evidence (and there were no other witnesses) to prove the charge of murder:

Kyle, you're bluffing. You gambled on getting a confession and you didn't get it. I know now you haven't got one iota of actual evidence against her, and without any witnesses, you'll never be able to prove it couldn't have been an accident.

Dismiss that phony attempt charge.
Change murder to manslaughter and we'll plead guilty, providing you give a recommendation for leniency.

Sackett makes a two-pronged motion that is then granted by the judge:

• to dismiss the charge of attempted murder (of Frank), and
• to permit the defendant to withdraw her original plea of guilty to murder (of Nick), for the purpose of entering a new plea of guilty to manslaughter

Cora's plea is changed to guilty - to a lesser charge of manslaughter, and she is sentenced to be "confined in the state institution for women at Tehatchapie for the term prescribed by law." Sackett's recommendation for leniency results in her sentence being reduced to probation, suspending execution of the sentence. Cora is acquitted and freed. Frank comforts her: "It's all right, Mrs. Smith. Everything's gonna be all right now." Cora is seething with hate for Frank: "That's what you think." Although Sackett compliments Keats for a "brilliant piece of strategy," he isn't going to give up: "You're crazy if you think I'm through with those two murderers."

Frank and Cora are driven back to the cafe by Keats - and told how he knew that Sackett was bluffing. "If the insurance company with the smartest detectives in the world couldn't find any evidence of murder, then it's a cinch that the DA couldn't." The cocky lawyer presents Cora with the insurance policy payoff of $10,000, while taking more pleasure from winning his $100 bet with Sackett: "I'm gonna frame it and hang it right over my desk."

Now that their relationship is poisoned with distrust and they are turned against each other, Cora wants to be rid of Frank: "Well, goodbye, Mr. Yellow. I don't know what you're going to do and I don't care. But I'm going in and open up my lunchroom." Cora wants to be respectable and well off, rather than on the road and wandering away with Frank. He is permitted to stay, although the two lovers are very divided:

Frank: Cora, Cora, look. Maybe, maybe you could sell the place and we can go away somewhere and start fresh, where nobody knows us.
Cora: Oh, no! You've been trying to make a tramp out of me ever since you've known me. But you're not going to do it. I stay here.
Frank: All right. I'm gonna stay too.
Cora: Well, let me tell you something. If you do stay, there's gonna be a lot of hard work done around here because I've got ideas for this place. I'm gonna fix up a nice spot out there under the trees and then I'm gonna get a license to sell beer...
Frank: You're in the hamburger business...
Cora: Can't you get it through your head that I'm gonna amount to something? So, if you want to keep your job, you'll have this place cleaned up and open for business tomorrow morning at seven.
Frank: OK. OK, Mrs. Smith.
Cora: That expresses it perfectly.

Cora's notoriety from the trial helps the business to prosper and flourish at Twin Oaks:

Things stayed that way for several weeks. I had to watch her like a hawk because I didn't trust her for a minute. People started flocking out to the Twin Oaks just to see what she looked like.

After a few weeks, Keats arrives to speak to Cora, recommending that she marry Frank for respectability's sake, because of the growing gossip about them:

Keats: The folks around here are talking about you two living here like this.
Cora: Talking about it, hah!
Frank: That's a laugh.
Keats: Is it? An unmarried man and woman living together under the same roof? Why in Los Angeles not long ago, they held a murder suspect and when they couldn't hang it on him, they threw him into the can under forty-seven different laws.
Cora: I'm way ahead of you, Mr. Keats. And I'll handle this.

At their justice of the peace marriage in Los Angeles, Cora's lipstick ends up on Keats' cheek, not Frank's - the couple's enmity and cynicism toward each other has grown:

Keats: What flavor do you call it, Frank?
Frank: I can't remember that far back.
Cora: As far as I'm concerned, you imagined it even then.
Frank: Oh, dry up.
Cora: Notice his neck-tie, Mr. Keats. It's my wedding present to him. But the way he wears it, you'd think it was a noose around his neck.
Keats (proposing a toast): Well, I can only think of fifteen or twenty reasons why you two should never be happy.

After learning of her mother's heart-attack, Cora takes the train from E. Los Angeles for a week's visit to her home in Iowa after a three year absence. Still seething at her new husband, she refuses to have Frank escort her to the departing train: "I hate goodbyes." Since Frank is "in a bad way," he wants to "see if I can't get that blonde out of my system." He flirts with a red headed young girl named Madge Gorland (Audrey Totter) with a stalled car in the train's parking lot. Coincidentally, she works at Joe's Highway Haven, a lunchroom - "a member of the club." He makes advances with a well-worn pick-up line: "With my brains and your looks, we can go places," and invites her to go across the border to Tijuana, Mexico. The weak-willed bridegroom provides a familiar description of himself: "My feet. They keep itchin' for me to go places." Madge shares an affinity with his gypsy spirit:

Madge: You're an outlaw. Can't stand captivity. Me too. I get so sick of hamburgers sometimes, I--...What time will we get back from Mexico?
Frank: Oh, uh, I got a whole week. Come on, slide in.
Madge: All right.
Frank: I'll bet you got a little gypsy in you.
Madge: They say I was born with rings in my ears.
Frank: Well, maybe a week won't be long enough and Mexico won't be far enough. (Frank throws his wedding tie into the glove compartment as he embarks upon a faithless affair)

A week later, a black-clothed Cora returns from her mother's funeral, telling Frank about the death for the first time: "I didn't want to bother you with it." She is a changed woman and more optimistic about their future together, but surprised that he is driving a U-Drive car:

Cora: Oh, I have a lot to tell you, Frank. I think you and I are going to get along much better from now on.
Frank: Well, what is it?
Cora: No, not now, tonight maybe after dinner.

When they get back to the cafe, Keats' unscrupulous gumshoe Kennedy (who had transcribed the confession but kept it from the prosecutor) blackmails them for an outrageous $12,000 for the forced confession: "That paper, the one I wrote up for you, Mrs. Chambers...Was still in the files when I left Keats so I took it. I was thinkin' maybe you'd like to get it back." If they won't agree, "the confession goes to Sackett." Cora cozies up to Kennedy to disarm his gun: "It's really too bad that Frank was here, because if we had been alone, I feel that, uh, I could have talked you out of it." She tosses her beer in his face, and Frank finishes him off with repeated punches and a knee to his bloodied face. At gunpoint, Kennedy calls one of his "friends," Willie (A. Cameron Grant), to bring the "papers" out to the cafe.

Both Cora and Frank ambush Willie when he arrives to deliver the confession, securing the "photostats and the negative." Frank burns "the last of the photostat" in the fireplace. Cora's memory also holds millions of photostats "and just one of them is enough for Mr. Sackett." She cannot be tried again for the same crime, but she can denounce Frank to Mr. Sackett and be rid of him - for his unnecessary affair with the redheaded Madge that she had just learned about:

Cora: Once they made it manslaughter, they can't ever do anything more to me.
Frank: What's the matter with you, Cora?
Cora: This! (She hurls his wedding tie at him) While you were wet-nursing Kennedy, your friend dropped in outside. So you're an outlaw and you just love Mexican food. Well, I hope your broken-down sweetie brings you plenty of it up to the death-house where I'm gonna send you...Don't worry, when it comes time to call in Mr. Sackett, I'll let you know. In the meantime, you just take it easy, cause you're gonna need all your strength.

Conversely, Cora is worried that Frank may retaliate against her to prevent her from turning him in: "Don't worry, when I get ready to skip out of here, I'll let you know. Just take it easy. You may need all your strength."

That's the way it kept up all day. Me following her around for fear she'd call Sackett. Her watching me like a hawk, for fear I'd...Both of us hating each other like poison. Finally she went up to bed. I went to my room, but I-I knew I didn't dare sleep. Then, all of a sudden...

Suspicious of each other's every move, both of them live in perpetual fear. To break the cycle, Frank discusses his foolish affair:

Frank: That other girl. She don't mean anything to me.
Cora: She told me you were going away with her.
Frank: Why didn't I? I planned to and I'll never come back. Why didn't I go away and never come back? Cause we're chained to each other, Cora.
Cora: Don't tell me you love me.
Frank: I do.
Cora: Oh, but love wouldn't mean a thing to me.
Frank: Do you hate me?
Cora: I don't know. But we've got to tell the truth for once in our lives.

As promised at the train station, Cora dramatically announces that she is pregnant with new life, and that she is worn out by repeated retributions:

Cora: Frank, I wasn't going to Mr. Sackett tonight. I was running away, for good, so that you wouldn't ever see me again. Me or, me or...
Frank: Cora.
Cora: No, no don't, Frank, I've got to tell you all about it. We, we took a life, didn't we, Frank? Well now, don't you see, we can give one back. And then maybe God will forgive us and maybe it will help square us.
Frank: Maybe it will. Maybe it will help. We've been all mixed up.
Cora: Oh Frank, I couldn't turn you into Sackett. I couldn't have this baby and then have it find out that I'd sent its father into that poison gas chamber for murder.
Frank: Was the baby the only reason?
Cora: No. Oh Frank, please, there's one thing I have to be sure of. No, don't ask me any questions. Just take me down to the beach. We've been so happy there and, and let's be happy again, just once more. And then I promise that everything will be settled one way or the other before we come back.
Frank: I'll get the car, Cora.

To cleanse themselves of guilt and recrimination, to forget the past, and to renew and re-affirm their love, they return to the beach where they first fell in love in the moonlight:

Cora: All the hate and revenge has left me, but is it all out of you?
Frank: I've been tryin' to find some way to prove it to ya.
Cora: Maybe I know a way. Let's swim out there, way, way out. Until we're so tired that we'll just barely be able to get back.
Frank: How is that gonna prove...?
Cora: Oh, please Frank. Come on. I'll show you.

When they are way out in the deep dark ocean and Cora tiredly struggles to stay afloat, she asks for him to either save her from drowning and pledge to restore their love, or leave her to perish. Frank rescues his exhausted lover:

Cora: What I wanted to be sure of was, whether you trust me, if you don't believe that I can ever turn on you again. And if you don't want me to go back with you, you could swim back by yourself. I'm too tired. I could never make it alone. Nobody'll ever know.
Frank: Cora, Cora. Don't say another word, darling. Save your strength. I'll take you in. (After they reach the shore and the car) Are you sure now?
Cora: I'm sure.

As the star-crossed lovers drive along the highway and near their home, Frank asks for a long-awaited kiss. Cora is painting her lips with lipstick:

Frank: I've been waiting a long time for that kiss.
Cora: When we get home, Frank, then there'll be kisses, kisses with dreams in them. Kisses that come from life, not death.
Frank: I hope I can wait.
Cora: Darling. (They kiss) Look out, Frank!

Distracted during a 'kiss that comes from life' while he is driving, he runs off the road, killing Cora ('with a kiss that comes from death') in a fatal auto accident. The car door opens after the crash - Cora's lifeless arm falls off the seat, and a tube of lipstick slowly drops to the floor of the car and onto the ground. [In life and death, Cora is identified with a glossy symbol of glamour - a lipstick tube.]

The headlines of the paper read:

GRAND JURY INDICTS CHAMBERS AS SLAYER: Killed Wife In Bogus Auto Accident, Charged to Face Murder Trial - Sensational Cora Smith Case Has Aftermath in Action against Husband

Frank is tried and convicted for Cora's murder. Sackett argues in court that Frank was guilty all along - if not solely for Nick's murder, then for Cora's murder:

This man, Frank Chambers, and the dead woman, first murdered her husband to get his estate. And then Chambers murdered her so that he would have it all to himself.

In his death cell in prison, after being blamed for her murder and awaiting execution, Frank receives full retribution and punishment for his adulterous crimes. The soon-to-be executed criminal explains to the priest Father McConnell (Tom Dillon) how he still truly loves Cora. He also doubts whether she knew of his love in her final moments of life:

Frank: The jury was out five minutes. The judge said in sentencing me that he was giving me the same consideration he'd show any other mad dog....And now Father comes an important thing you can do for me. Do you think she knows?
Father: Knows that you didn't kill her?
Frank: She must know it. But that's the awful part when you monkey with murder. Somehow, maybe, it flashed to her head when the car hit that maybe I did do it. Father, do you think she knows the truth?
Father: We can hope.
Frank: We got off to a wrong start. Somehow or other, we never got back on the right track. But I-I didn't kill her. I loved her so much. I tell ya, I would have died for her.

The governor refuses to give Frank a reprieve from execution in the gas chamber. Frank shows terror in his face that he is on death row and that he has been falsely accused of Cora's murder: "I didn't do it, I didn't do it...I'm not going to go in the gas chamber for killing her!" Fate (the figurative 'postman') has determined that both he and Cora will pay in the long run - thus explaining the title of the film:

Sackett: Suppose you got a stay of execution, a new trial, and acquittal of killing Cora. Then what? Last night, they auctioned off the fixtures of the Twin Oaks. The man who bought the cash register found a note in the back of the drawer. He brought it to me. It's addressed to you. Cora wrote it. It's a very beautiful note, Frank, written by a girl who loved a man very much. I imagine it was written earlier the very night she died. A note of farewell, isn't it?
Frank: She did try to run away that night.
Sackett: And since she had no idea anyone would ever see that note but you, it therefore has in it just enough of a confession to convict you of helping her kill her husband. So, if you were to leave this room because you didn't kill her, you'd soon be right back here again for helping her kill Nick. What's the use?
Frank: Then, then what's gonna happen to me is not because I killed her?
Sackett: No, laddie. For killing Nick.
Frank: You know, there's somethin' about this that's like, well, it's like you're expectin' a letter that you're just crazy to get. And you hang around the front door for fear you might not hear him ring. You never realize that he always rings twice.
Sackett: What's that?
Frank: He rang twice for Cora. And now he's ringing twice for me, isn't he?
Sackett: That's about it.
Frank: The truth is, you always hear him ring the second time, even if you're way out in the back yard.

Not wanting Cora's spirit to think he did away with her, in the last lines of the film, Frank accepts his fate with one final prayer request. He reasoned that he would pay with his life for a crime he didn't commit, making up for getting away with the murder of Cecil. In the ironic ending, Frank asks the priest to make things right with Cora so that she will know that her murder was only an innocent accident:

Father, you were right. It all works out. I guess God knows more about these things than we do. Somehow or other, Cora paid for Nick's life with hers. And now I'm going to. Father, would you send up a prayer for me and Cora, and if you could find it in your heart, make it that we're together, wherever it is? (The priest nods)