The medical examiner confirms that the murder victim "who was bumped off upstairs" was Diane Redfern. [Diane was shot in the face with the shotgun, preventing proper identification.] Against the detective's strict orders, Laura phones Shelby and they decide to meet in front of Bullitt's. Their conversation is tapped by police in the apartment's basement, and McPherson is miffed by the "dame's" evasiveness:

Dames are always pulling a switch on you.

After Laura meets with Shelby, McPherson tails his prime suspect to Laura's country home. During the confrontation, he catches Shelby with a recently-fired shotgun in his hands. According to Shelby, it was given to Laura "for protection - she didn't want it but I insisted. This house is rather isolated as you see." Determined to find the killer (and to eliminate one of his potential rivals for Laura's love), McPherson delves deeper into Shelby's shady actions the night of the murder and forces him to tell the truth:

You took that poor girl in Miss Hunt's apartment. You knew all along it was she who was murdered. Didn't you know Laura Hunt would come back any day and spill the whole thing? Or did you plan to kill her too and hide the body someplace and cover up your first crime?...You took a bottle of Black Pony to her house Friday night...Where's the key to her apartment?

When pressed, Shelby confesses that he used a duplicate key from Laura's office, and snuck Diane Redfern (who thought she was in love with him) into Laura's flat, presumably to talk to her and break off their affair. When the doorbell rang, Shelby remained in the bedroom and asked Diane to answer the door, preparing her with the excuse that Laura had lent her the apartment for the weekend. Fearing for both himself and Laura following the shotgun blast, and panicked by the death, he fled the scene and remained quiet:

Then there was a moment's silence and then a shot. It was an awful explosion. By the time I reached her, the door was closed. She lay there on the floor....I was too confused, too horrified, incapable of doing anything. The room was dark. I saw only a vague heap lying on the floor. I don't think I fully grasped the situation. I think I called her name, but I'm not sure. I-I remember kneeling on the floor, feeling her heart. My first instinct was to call the police....I was afraid, not only for myself but for Laura. In a panicky sort of way, I felt that I must keep out of this to keep Laura out of it. Oh, I know now how foolish and hopeless it was, but there was only one thing on my mind - the safety of a person whose life was dearer to me than my own. Don't you understand that?

Shelby claims that he doesn't know who the murderer is, and doesn't admit that he suspects Laura: "I was groping for some way to keep Laura's name out of it. I was heartbroken about Diane and panic-stricken about Laura. I haven't slept a full two hours since this thing happened." Dismayed, McPherson tests Laura's radio and finds it fully functioning: "I hoped it wouldn't," he mutters to himself.

The next morning, McPherson arrives at Laura's (his fourth visit) with a bag of groceries, intending on sharing breakfast with her. Laura's maid Bessie arrives and is shocked and hysterical when she sees Laura alive (a "ghost"). Laura calms her down: "Have you ever heard a ghost ask for eggs?" To explain why she disobeyed him the night before when she phoned Shelby, Laura describes herself as ambitious, assured, confident, and freedom-loving:

I never have been and I never will be bound by anything I don't do with my own free will.

Shelby arrives with flowers for Laura and their engagement is declared "on again." After a visit to his lawyer, Shelby protests that anything he admitted the previous night to the detective was made "under duress and can't be used" against him - "besides, none of it was true." Waldo also arrives and faints dead-away, off-camera, when he first sees the resurrected Laura. Lydecker is revived after the "terrible shock" - he asks the detective about Laura's reincarnation:

Lydecker: Well, McPherson, what does Laura's resurrection do to you?
McPherson: Too bad Diane Redfern can't be resurrected.

Lydecker plans a homecoming and invites many of Manhattan's upper crust to celebrate Laura's return, challenging McPherson to use the occasion to solve his case: "Perhaps our friend can weave all the loose ends into a noose, eh, McPherson?" McPherson has already arranged for a confrontation by inviting all the suspects: "Sorry you went through all that trouble. I've already called them."

At the festivities of the indolent rich, Anne can hardly conceal her disappointment that Laura is still alive. She desperately proposes marriage to Shelby, but he declines because of his romantic involvement with Laura:

Shelby, why don't you come to your senses? You know it's all over between you and Laura or it soon will be. You haven't lost me. Why don't we get married - now?...You need me. We'll get the best lawyer that money can buy. And when it's all over, we'll go away - anywhere you want - and forget about all this.

Shelby pushes away Anne's proposition by telling her that "Laura needs me." He then advises Laura about the devious motivations of McPherson's tactics to get close to her: "I see he's taking a new tact...Trying to make you like him, to make you talk." Indeed, Shelby thinks Laura murdered Diane Redfern with the shotgun at the country home that he had earlier given to her: "You don't have to lie to me, darling. I'll stand by you."

To drive a further wedge between Shelby and Laura - and bring like-minded Shelby to herself, the lonely and desperate Anne encourages Laura's budding interest in McPherson: "Are you as interested in McPherson as he is in you?" She admits the weak-charactered affinity she shares with Shelby ("We belong together because we're both weak and can't seem to help it"). Anne and Shelby are both decadently corrupted by their upper-class acquisitions, money and their own worldliness, and capable of committing the murder - under the right circumstances:

McPherson suspects Shelby...Oh, I don't think he did it, but he's capable of it....Anybody's better for you than Shelby. Anybody is. Shelby's better for me...'cause I can afford him and understand him. He's no good, but he's what I want. I'm not a nice person, Laura, and neither is he. He knows I know he's just what he is. He also knows that I don't care. We belong together because we're both weak and can't seem to help it. That's why I know he's capable of murder. He's like me.

Laura turns back suddenly toward Anne - realizing that her aunt could have been the murderer at her door with a shotgun. Anne had thought of killing her favorite niece over her faithless lover, but didn't:

No dear, I didn't, but I thought of it.

During the party, McPherson promises on the phone (within everyone's earshot) to police headquarters that he will solve Laura's murder: "Don't worry. I told you I'd bring in the killer today. Yeah, I was just gonna make the arrest when you called. No, I can't tell you now. I'm not alone. You'll see when I come in." The ploy works - he walks by each of the major suspects, pauses, and then arrests Laura. To possess her himself, he chooses Laura as his prime suspect. Bessie and Lydecker step forward to defend her:

Lydecker: Don't worry, darling. Let them accuse you. We'll fight them. I have every weapon. Money, connections, prestige, and my column. Every day, millions will read about you and rally to your defense.
McPherson: You talk as if you wanted to see her tried for murder.
Lydecker: Yes, rather than let you blacken her name with suspicions and rumors. Try to prove her guilty. Get on the witness stand with your poor shreds of evidence. I'll expose your cheap methods you used on her.

Shelby cautions and warns Laura about "this fella" McPherson. Insulted, the detective strikes back: "It's too bad you didn't open that door Friday night, Carpenter" and punches Shelby in the stomach. Slumped over in an armchair, Shelby holds his bruised mid-section, while Anne cradles his head in a motherly fashion: "Oh, did he hurt you, darling?" He gives her hand a wet kiss - [the couple does "belong together"!].

McPherson escorts Laura to a bare room at the police headquarters [in sharp contrast to the settings where the upper-class New Yorkers live and play]. Two lights are positioned to glare on Laura's face. In a tough interrogation, McPherson grills her about what she has been holding back: "Let's have it."

Laura: What difference does it make what I say? You've made up your mind I'm guilty.
McPherson: Are you?
Laura: Don't tell me you have any doubts?...No, I didn't kill Diane Redfern or anyone else.
McPherson: Then why, why did you tell me the radio at your country place was broken.
Laura: Because it was broken.
McPherson: Not when I tried it.
Laura: Just as I was leaving the village, I asked the local handyman to fix it.
McPherson: How did he get in?
Laura: I always leave a key under the flowerpot on the porch.

His main motivation in having her alone for questioning is to learn whether she is really devoted and in love with another suspect and romantic rival - Shelby Carpenter:

McPherson: The main thing I want to know is why you pulled that switch on me about Carpenter. You told me last night you decided not to marry him.
Laura: Yes, I guess I did.
McPherson: But today, it was on again. Why?
Laura: Well, I-I changed my mind.
McPherson: (exasperated, he moves in front of her face) What are you trying to hide? Don't you realize you're involved in a murder? You've got yourself in a jam that's not gonna be easy to get out of unless you're on the level with me.This is no time for secrets. Now, did you really decide to call it off? Or did you just tell me that because you knew I wanted to hear it. What went on between you and Carpenter when you saw him last night? Did he persuade you to make up? Or did you agree to pretend you had? Was that it?
Laura: Well, we, that is, both of us ---
McPherson: He convinced you that if you broke the engagement now, people would think you believed he was guilty.
Laura: Yes. But now I know it was only because he thought I was.
McPherson: Did you believe he was guilty?
Laura: No, I'm sure he isn't. But he'd gotten himself into an awfully suspicious position. And he's the sort of man that people are always ready to believe the worst about.
McPherson: Are you in love with him?
Laura: I don't see how I ever could have been.
McPherson: (pacified) Come on, we're going home.

Although McPherson is convinced of Laura's innocence, his own love for her has prompted him to use "official surroundings" to question her and reach clarity on the case - and really prove her innocence. In "some sort of a game," McPherson doesn't even book or charge Laura - he brought her there only to erase the last of his doubts about her innocence: "I was 99% certain about you. But I had to get rid of that 1% doubt...I'd reached the point where I needed official surroundings."

McPherson proceeds to the apartment of another major suspect - Lydecker. Since Lydecker is still at the party, he finds Lydecker's place vacant. When he hears the antique grandfather clock chime, he realizes, from his notes, that it is identical to the one Waldo had given Laura (the one that Lydecker wished to remove from the premises). He crouches down and breaks into its hollow base - it's empty. On a hunch that the space could hold the missing murder weapon, he rushes away.

After being interrogated, Laura has returned to her own apartment, where an incensed Lydecker, more possessive than ever, is occupied with convincing her to stay away from the possible consummation of a relationship with McPherson (a rival - an attractive man with a "lean strong body"). As she vows that "no man is ever going to hurt me again," Lydecker explains why he desperately wants her for himself [his jealousy is unusual, given his homosexual leanings]:

Lydecker: It still doesn't make sense to me, Laura. He's playing some sort of a game with you.
Laura: I don't think so.
Lydecker: I don't deny that he's infatuated with you in some warped way of his own. But he isn't capable of any normal, warm, human relationship. He's been dealing with criminals too long. When you were unattainable, when he thought you were dead, that's when he wanted you most.
Laura: But he was glad when I came back as if he were waiting for me.
Lydecker: Do you know what he calls women? 'Dames.' 'A dame in Washington Heights got a fox fur out of him.' His very words.
Laura: That doesn't mean anything. He isn't like that.
Lydecker: Laura, you have one tragic weakness. With you, a lean strong body is the measure of a man. And you always get hurt.
Laura: No man is ever going to hurt me again. No one. Not even you.
Lydecker: I? Hurt you? Laura - (he turns her around) look at me. When a man has everything in the world that he wants, except what he wants most, he loses his self-respect. It makes him bitter, Laura. He wants to hurt someone as he's been hurt. You were a long time finding out about Shelby but that's over now. We'll be back together again.

McPherson enters, unannounced, without ringing the doorbell. He offers his own "personal opinion" that Laura is innocent. Lydecker is at the height of his possessive jealousy over McPherson (in Laura's presence), and is peeved and embittered by McPherson's masculinity, earthiness, and easy sexuality. When Lydecker attacks McPherson, Laura sides with Mark. Lydecker congratulates them on "what promises to be a disgustingly earthy relationship":

Lydecker: It's the same obvious pattern, Laura. If McPherson weren't muscular and handsome in a cheap sort of way, you'd see through him in a second.
Laura: Waldo, I mean to be as kind about this as I know how. But I must tell you. You're the one who follows the same obvious pattern. First it was Jacoby, then Shelby, and now I suppose - I don't think we should see each other again.
Lydecker: You're not yourself, darling.
Laura: Yes I am. For the first time in ages, I know what I'm doing.
Lydecker: (snootily) Very well. I hope you'll never regret what promises to be a disgustingly earthy relationship. My congratulations, McPherson. And listen to my broadcast in fifteen minutes. I'm discussing Great Lovers of History.

Laura brusquely breaks off her long-standing relationship with Lydecker. Waldo apparently leaves the apartment in a huff, but then hesitates outside on the stairway - where his body casts a shadow on the wall. Laura admits how painful it was to turn Lydecker away: "It was the most difficult thing I ever had to do in my whole life." Unromantic but realistic, McPherson is still focused on the search for clues: "All I need is the gun." He tampers with the base of Laura's grandfather clock, the one identical to Lydecker's, and the door pops open - the evidence to incriminate Lydecker is revealed. The murder weapon is concealed inside the grandfather clock given to Laura by Waldo. McPherson removes the bullets and then describes the murder sequence - positing Waldo as 'Laura's murderer' because he couldn't bear losing her to Shelby (no one else would be worthy of her):

The doorbell rang and Diane Redfern went to the door in your negligee. She opened the door. The room was dark. Waldo saw a girl standing there and he assumed it was you. He figured that if he couldn't have you himself, he was gonna make sure that nobody else did, so he let her have it with both barrels right in the face. She fell here. Waldo heard Shelby running from the next room so he hid in the stairway outside. Shelby was scared so he ran out as fast as he could. Then Waldo came back and placed the gun in that clock.

Although unwarranted, Laura takes the figurative blame for Diane's murder:

He didn't really kill Diane Redfern. I killed her...I did as sure as if I'd pulled the trigger myself...I'm as guilty as he is. Not for anything I did but for what I didn't do. But I couldn't help myself. I owed him too much.

McPherson can sympathize with everything except her protective feelings for Shelby: "I can't understand why you've tried so hard to protect Shelby these last few days." Laura knows from experience the 'murderous' intentions of Waldo toward her male suitors (she speaks loudly enough for him to hear her outside in the hallway): "I was nearly frantic with fear you'd arrest Shelby. I knew he wasn't guilty. He hasn't enough courage to kill a fly. And Waldo was doing everything he could to incriminate him. It was his way of getting rid of Shelby just as he did Jacoby." With a perfect deadpan delivery, the cop tactlessly judges her male, ne'er-do-well friends:

For a charming, intelligent girl, you certainly surrounded yourself with a remarkable collection of dopes.

When McPherson leaves to arrest Waldo, they share a good-night kiss at the door as he departs: "Get some sleep. Forget the whole thing like a bad dream." When Laura is left alone, Waldo sneaks back into her apartment, past the ticking grandfather clock. He is about to murder Laura (for the second time!) because she has fallen in love with McPherson and is not returning his love. Lydecker removes the shotgun from the clock's base, reloads the murder weapon, and becomes startled when he hears his own mellifluous voice on a pre-recorded radio broadcast that Laura plays within her bedroom. Lydecker's sick fantasy is echoed in his own poetic broadcast about how Love lasts beyond death:

And thus, as history has proved, Love is Eternal. It has been the strongest motivation for human actions throughout centuries. Love is stronger than Life. It reaches beyond the dark shadow of Death. I close this evening's broadcast with some favorite lines...Brief Life - They are not long, the weeping and the laughter, love and desire and hate. I think they have no portion in us after we pass the gate...They are not long, the days of wine and roses. Out of a misty dream, our path emerges for a while, then closes within a dream.

In her bedroom as Laura prepares to retire, Lydecker breaks her out of her reverie and shocks her with his appearance. He vows to kill her, rather than leave her to the "vulgar pawing of a second-rate detective":

Lydecker: That's the way it is, isn't it, Laura?
Radio Announcer: 'You have heard the voice of Waldo Lydecker by electrical transcription.'
Laura: (begging) Waldo, you've taken one life. Isn't that enough?
Lydecker: The best part of myself - that's what you are. Do you think I'm going to leave it to the vulgar pawing of a second-rate detective who thinks you're a dame? Do you think I could bear the thought of him holding you in his arms, kissing you, loving you? (McPherson has returned with the police force and is ringing the doorbell.)
Lydecker: (as he raises the shotgun) There he is now. He'll find us together, Laura as we always have been and we always should be, as we always will be.

His words strongly imply that he intends a murder/suicide ("He'll find us together, Laura as we always have been and we always should be, as we always will be.") Laura deflects the aim of the shotgun as it goes off. McPherson breaks down the door just in time to save her and have her run and fall into his arms. Waldo is mortally wounded in an exchange of gunfire with the police. A shotgun blast goes wild and shatters the face of the grandfather clock. As Waldo is dying and utters her name in his final words, she rushes to his side. The camera rests on the clock as Lydecker's final words are delivered off-screen with a theatrical flourish - [is it the conclusion of his radio show?]:

Goodbye, Laura. Goodbye, my love.

THE END rests above the haunting portrait of Laura.