In the police conference room the next day, Nick is asked to consult with Beth, Dr. Myron (William Duff-Griffin) and Dr. McElwaine (James Rebhorn) on a psychiatric evaluation. He is questioned about his "difficulty controlling" his temper by Dr. McElwaine, and he makes a mockery of the psychological questioning before stalking out of the room:

McElwaine: Nick - when you recollect your childhood, are your recollections pleasing to you?
Nick: Number one: I don't remember how often I used to jerk off, but it was a lot.
Number two: I wasn't pissed off at my dad, even when I was old enough to know what he and mom were doing in the bedroom.
Number three: I don't look in the toilet before I flush it.
Number four: I haven't wet my bed for a long time.
Number five: Why don't the two of you go f--k yourselves? I'm outta here.

Beth hesitates and then follows Nick down the corridor, catching up with him:

Beth: (angered with him) What is your problem? I'm trying to help you. Why won't you let me help you?
Nick: I don't want your help. I don't need your help.
Beth: Yes, you do. Somethin's going on. (pause) You're sleeping with her, aren't you?
Nick: What's this interest you've got in her?
Beth: My interest is in you, not her. She seduces people. She manipulates people. She'll do anything she can---
Nick: I thought you hardly knew her.
Beth: I know the type. I'm a psychologist.
Nick: (He grabs her roughly as they stop in the hallway) That means you manipulate people TOO, Beth. You're a practicing psychologist -- you're better at it than she is.
Beth: I feel sorry for you, Nick.

He drives back to the beach house - the white car is parked in the driveway. The black car is missing. Roxy will no longer be a rival for Catherine's love. Everything is quiet and dark. Nick finds Catherine upstairs, sitting in a rocking chair that faces the window looking out on the water. She is upset, and haltingly describes her understanding of Roxy's motivation to kill him - jealousy:

Catherine: I should have known. I came into the house. We were down on the beach. She looked at me so strangely. She left right after you. I-I shouldn't have let her watch us. She wanted to watch me all the time. (She looks at Nick) She tried to kill you, didn't she?
Nick: Did you like her to watch?
Catherine: Do you think I told her to kill you? (He shakes his head no) Everybody that I care about dies. (He kneels and kisses her on the forehead. She sobs in his arms.) Make love to me.

After another round of sex in the beach house, they peacefully lie together in front of a roaring fire under a blanket. Nick suggests that Roxy killed Johnny because she was jealous of Johnny too. Catherine dismisses the idea, because Roxy her lover, wouldn't set her up and "she never got jealous before. She got excited." Nick doesn't know why everyone around Catherine dies.

And then, Catherine casually talks about her days at Berkeley - confessing crucial information about her background:

I don't have luck with women. There was this girl I met when I was in college. I slept with her once. She started following me around taking my picture. She dyed her hair, copied my clothes. Lisa - something - Oberman. It was awful.

The next morning in the Police Department in Cloverdale (Roxy's last known address), Nick and Gus flip through police photos of the deceased Roxy as a young juvenile offender, and they view large color photographs of two murdered brothers that she had killed "on impulse" (at age sixteen) with a razor - there was no motive except jealousy. [Roxy's juvenile records of fratricide had been sealed and only became available after her death.] Gus sees a connection with the murders the paroled Hazel Dobkins committed, and that both family-killing females are associated with Catherine: "Just like Hazel Dobkins fixed her whole family." Although Gus swears that Catherine is guilty by association ("You ever met a friend o' hers hasn't killed somebody?"), Nick defends: "I'm not sure anymore she did it." Gus believes Nick's sexual passion has clouded his brain: "Well hell, she got that magna come lawdy p---y on her that done fried up your brain."

Nick heads over to UC Berkeley and the Office of the Registrar to look at the school records for 'Lisa Oberman' - but there never was a Lisa Oberman registered at the school. Outside Catherine's San Francisco home, Nick finds Catherine leaving with Hazel Dobkins. In private, he cynically criticizes Catherine's befriending of psychopathic murderers: "You like to hang out with murderers, or what? Did you know that Roxy...?" Catherine explains that she gets characters and ideas for her books from real-life killers: "Yes of course I knew. Look. I write about unusual people. And sometimes when I do my research, I get involved with them. It happened with you. (She gives him a thin smile and then takes his cigarette out of his mouth before kissing him.) Killing isn't like smoking. You can quit."

Before Catherine drives Hazel home, in time to watch her favorite TV show, 'America's Most Wanted,' Nick asks one more firm question: "There was no Lisa Oberman when you were at Berkeley." Angered that he is checking up on her, she gives him another last name as she accelerates away: "I said Hoberman." Nick checks the police department's computer screen for a DMV License Check on Lisa Hoberman. The words appear from left to right: "1987 RENEWAL - - ELIZABETH GARNER, 147 Queenston Dr., Salinas, CA 92358." Lisa Hoberman and Elizabeth Garner are the same person! The 1983 license shows the photo of a young "Lisa Hoberman" - ablonde-haired Beth Garner who lived in Berkeley at 11431 Euclid Ave., Apt. 2-C.

In Beth's apartment that same evening, Nick confronts her with his knowledge that there was an association between Catherine and 'Lisa/Beth' at Berkeley. Beth puts her own spin on the story, reversing the roles, and downplaying her own bisexuality:

Beth: I slept with her once in school. I was just a kid. I was experimenting. It was just that one time. She developed a fixation on me. She styled her hair like mine. She wore the same kind of clothes I did. It scared me. Isn't that what she told you?
Nick: She said it was you. (He points at her) You dressed like her, you dyed your hair blonde.
Beth: I did dye my hair. It had nothing to do with her. I was a redhead for a while, too.
Nick: Did you know Noah Goldstein?
Beth: I had him for two classes.
Nick: You saw all the reports, Beth! Phil copied you and you never said anything.
Beth: Well, what am I supposed to say? Hey guys, I'm not gay, but I did f--k your suspect! I was embarrassed. It was the only time I've ever been with a woman. She's really sick, you know. Do you know what she's doing? She knows I went to Berkeley. She knows I knew Noah. She makes up this story about me. She's handing you somebody who's obsessed with her.
Nick: She didn't hand you to me. She doesn't even know who you are. She told me about a, a Lisa Hoberman. 
Beth: She knows you'd find out who Lisa Hoberman is. You're a good cop. Did she tell you casually and make it seem irrelevant? Did she tell you in bed, Nick? That's what I'd do.
Nick: Why did you change your name?
Beth: I got married. He called me Beth. He was on staff at the clinic down in Salinas. It didn't last long. (He reacts with disbelief) Nick? God, do you really think that I could kill someone? I mean, I never even met Johnny Boz. What about Nilsen? What possible motive would I have to kill Nilsen?...She's evil, she's brilliant.

When he gets back to his own apartment, Nick's head is swimming - he doesn't know who to believe. Catherine scares him from behind when she puts her hand on his shoulder. He wants to quit playing games and explains how 'Lisa Hoberman' told him the exact opposite story: "She said you got it backwards. She said you even styled your hair like she did." Catherine adds another fact for the skeptical cop to assert her credibility: "I had to go down to the campus police and file a report about her. I suppose you still think I kill people too, right?"

In the campus police records room at Berkeley, Nick is told that the report about Lisa Hoberman dated 1980 was loaned out (for the whole last year) to Lt. Nilsen. On the pier as Gus and Nick walk together by S.F. Bay, Nick describes one possible scenario from the evidence - Beth's violent past, bisexuality and secret deviant obsession with Catherine could explain her motivation. Gus can't understand why his friend staunchly defends Catherine - an obviously-guilty girlfriend:

Nick: If Beth killed Johnny Boz to frame Catherine, she wouldn't want anybody to know what happened at Berkeley. But Nilsen found out about it. And that gives her the motive to kill him....
Gus: She'd have to be nuttier than a twenty-pound Christmas fruitcake. She's not the one who hangs out with multiple murderers - your girlfriend is.
Nick: She's a writer, all right. That's her job.
Gus: I don't buy it. There's gotta be somebody at Berkeley who knows what the hell happened.
Nick: (yelling) I know what happened, all right. Catherine told me. And everything she says has checked out.
Gus: You've got God-damn tweety birds flutterin' around your head, that's what you've got. You think you can f--k like minks, raise rugrats, and live happily ever after? Oh, man!

When Nick gets back to his place, Catherine has already let herself in, and given him a large fern plant as a present: "I decided to give you a second chance," she purrs. "I missed you." She moves in closely behind him, grabs his rear, and asks a second time if he missed her. With a determined goal to get him sexually aroused, she removes her top and reveals her ripe breasts in front of him:

Nick: I've seen 'em before.
Catherine: Yeah, well you might not see them again. My book's nearly finished. (He can't resist - he moves forward and touches her breasts) My detective's almost dead.
Nick: So I've got time for a last cigarette?
Catherine: Afterwards. (They kiss each other passionately)

The scene cuts to the two of them sitting in the window seat while sharing a cigarette - naked. His back is to the wall, and she leans against him. He has his legs around her. His next day's work is to "do some research," and to help him, she suggests a better, more realistic ending:

Catherine: What are you researching?
Nick: A new ending to your book.
Catherine: Oh really? What's the twist?
Nick: Well, the detective falls for the wrong girl, but he doesn't die.
Catherine: So what happens to them?
Nick: They f--k like minks, raise rugrats, and live happily ever after.
Catherine: It won't sell.
Nick: Why not?
Catherine: Somebody has to die.
Nick: Why?
Catherine: Somebody always does.

On his own, Nick drives to the small Salinas Medical Clinic in the Salinas Valley about 100 miles south of San Francisco, and asks to see Dr. Joseph Garner - Beth's husband. Nick is told that the doctor died about five to six years earlier - "he was shot." While the local Monterey County Sheriff is spraying off his car, he tells Nick that Dr. Garner was the victim of a drive-by shooting as he walked home from work - the murder weapon was a .38 revolver that was unrecovered: "No suspects, no motive. Unsolved." The sheriff stops spraying when asked: "Was his wife ever a suspect?" He recalls that another SF police detective about a year earlier had asked him the same exact question - his name was Nilsen. Although "there was some talk" that SHE "had a girlfriend," Beth Garner was never considered a suspect - "it never panned out."

Nick returns to Catherine's Stinson Beach house where he finds signs that she has finished her next novel, titled "Shooter" - the printer is churning out pages and the artwork for the cover is completed. He reads a few phrases on the printed page before Catherine enters:

Shooter raced into the...pounded the button for the...up the staircase...his partner's dead body...elevator, legs sticking out...

[In retrospect, the murder scene in the elevator at the end of the film perfectly matches this description in Catherine's latest book. Is she self-incriminating herself in the pre-meditated murder?]

Nick has finished his "research" and she has finished her "book." "So, how does it end, huh?", he asks. "I told you. She kills him," she replies. She coldly bids him goodbye: "Goodbye, Nick...Yeah, I finished my book. Didn't you hear me? Your character's dead. Good-bye. What do you want, flowers? I'll send you an autographed copy." He can't believe what she is saying about their relationship being over, and his frustrated anger bursts forth:

Nick: What is this - some kind of joke? Are you playin' a game here?
Catherine: The games are over. You were right. It was the f--k of the century, Shooter.

On a street near the Bay Bridge, Gus drives up and excitedly tells a shattered Nick:

Catherine Tramell's roommate freshman year - I just got a call from her. She's over in Oakland. Come on. (They drive away together toward Oakland) I've been phonin' people from her dorm all day. She must've heard I was tryin' to reach her. She says she knows all about Catherine and Lisa Hoberman....Here's somethin' else: Johnny Boz's psychiatrist has an office on Van Ness. Guess who he shares office space with? Dr. Elisabeth Garner.

When they arrive in Oakland, Gus starts off alone for the building where he is to meet 'Catherine Tramell's roommate" in suite 405. He pushes the elevator button to the fourth floor, but the elevator stops at the second and third floor on its way. Out in the car while waiting for Gus, Nick realizes that his partner is in grave danger - he jumps out of the vehicle and runs into the building. He pounds on the elevator button, but realizes that he can't wait for it. He races up the stairs to the fourth floor. As Gus emerges from the elevator when the door opens, he is savagely bludgeoned in the chest by an icepick-wielding hooded, blonde figure covered in a raincoat. In desperation, Nick hurries to the floor, but he is too late - he finds a blood-splattered Gus dying with his legs sticking out of the floor of the elevator.

Nick seizes Gus' gun from his holster and rushes down the hall to find the assailant. A shadow appears on the wall - he spins around and yells: "Freeze" - Beth moves forward. As Nick is screaming: "Put your f--king hands up," and "don't move," she calmly tells him: "I got a message on my machine to meet Gus here - Where is he?" He confronts her with more damning evidence as she moves forward, conspicuously holding something in her pocket:

Nick: I know about your husband. You still like girls, Beth?
Beth: What?
Nick: (screaming) Take your hand out of your pocket! Take it out!
Beth: What's wrong with you?

He fires, striking her in the chest. The impact propels her backwards onto the floor. In a whisper as she dies, she murmurs: "I love you." In her pocket is her key chain, not a weapon of any kind.

Lt. Walker and other police and forensics experts converge on the bloody scene, finding a zombie-like Nick frozen with regret. A blonde wig, hooded raincoat, and bloody icepick are found on the stair landing above the fourth floor. The raincoat has stenciled letters on the back: "SFPD." Later that evening, the homicide team checks Beth Garner's apartment, finding a .38 revolver in the bookcase behind some books. In the kitchen, the detectives find two of Catherine Woolf's paperback books ("The First Time" and "Love Hurts") and a collection of photos of Catherine with Johnny Boz and with her boxer husband. Lt. Walker concludes: "I guess that's it." Nick looks further at the photos - there are more shots of Catherine and Beth in the class of 1983 Berkeley graduation. [Were all the items, including the pictures, the gun and items on the stairway, planted by Catherine to frame Elizabeth?]

Follow-up investigations reveal that the raincoat was Beth's size, and she must have heard Nick and dumped the stuff on the stairway. There was no suite 405 in the building, and Catherine Tramell's roommate in her freshman year died of leukemia two years earlier. Nilsen's files are missing the Berkeley campus police report and any information about Salinas. The .38 found in Beth's apartment was the exact weapon used to kill Nilsen. The icepick was the same brand and model as the Boz weapon. Both of Beth Garner's answering machines had no message from Gus on them. The tape on her apartment answering machine was unused. Johnny Boz's psychiatrist remembered that Dr. Garner and Boz met at a Christmas party at his house a year earlier.

Curran is congratulated for his part in bringing down Dr. Garner: "You just can't tell about people, can ya? Even the ones you think you know inside-out...Congratulations, Curran."

In his dark and quiet apartment, Nick is greeted by a voice - it's Catherine who already knows about the murders: "I heard about what happened - on TV." He is expressionless as she makes a feeble attempt to deny her feelings for him, but she can't hold back her emotions:

I can't allow myself to care about you - - I can't allow myself to care - - I don't want to do this - - please - - I don't want to do this - - I lose everybody - - I don't want to lose you - - I don't want to lose you - - (they press together and hug each other)

The scene abruptly cuts to them making love in his bedroom. With tears in her eyes, they kiss each other, and she rolls atop him. As in all their other amorous couplings, she straddles him, stretches back, and begins rocking back and forth on his hips. As she climaxes, she reaches back, and then suddenly comes down on top of him - her whole body stretches across his - he is motionless. Is he alive? Has he been pierced with an icepick?

He lovingly reaches his arms around her. They lie next to each other in bed, both staring up. He is smoking a cigarette. She curls away from him toward the outer side of the bed:

Catherine: What do we do now, Nick?
Nick: We f--k like minks, raise rugrats. We live happily ever after.

Her right arm reaches over the side of the bed, as she retorts: "I hate rugrats." He revises his epitaph:

We f--k like minks. Forget the rugrats. And live happily ever after.

She half-turns and twists around, watching him turn his body away to put out his cigarette. The music builds - is she holding something in her hand? They look at each other for a long moment. She reaches out with her hand, pulling his neck and face toward her own body for another kiss. The screen darkens for a moment, and then returns.

[The finale of the ambiguous film arbitrarily leaves the inexplicable question of the guilt and/or innocence of the dangerous liaisons of the main characters up for grabs - did Catherine, in the ultimate mind/sex game, frame Elisabeth Garner with the murders? Or is Roxy the killer up until the time of her own death? Or did Catherine commit all of the murders herself? Or are all of them guilty in one way or another? ]

As Catherine and Nick kiss with more and more passion, the camera slowly descends down her side of the bed. When it lowers to the floor, the camera comes to rest with a close-up of the murder weapon - a thin, steel-handled icepick.