A New York City reporter named Rowena Price (Berry) meets her childhood friend Grace Clayton (Nicki Aycox), who wants her help in taking down Harrison Hill (Willis)—a wealthy advertising executive. Grace gives emails to Rowena which prove they had an affair that he recently ended.
A few days later, Grace is found to have been poisoned with belladonna and drowned. She was in her first trimester of pregnancy, and it causes Rowena to suspect Harrison's her killer. With the help of researcher Miles Haley (Giovanni Ribisi), Rowena goes undercover as a temp at his company, which begins a game of cat-and-mouse.
Perfect Stranger contains examples of:
- The Bad Guy Wins: Maybe. Rowena's the murderer—having set up Harrison to take the fall for Grace's death before killing Miles and framing him too. However, it's likely that a neighbor may have witnessed her latest murder.
- Big Bad: Harrison is heavily implied to be Grace's killer until The Reveal that Rowena did her in to end her blackmailing.
- Blackmail Backfire: Rowena murdered Grace because the latter was blackmailing her, and she goes on to kill Miles when he tries to blackmail her about framing Harrison.
- Book Ends: The film begins with a zoom-out of Rowena's eye—beginning with the inner layers, followed by the retina and the iris. It ends with another eye zoom-in, only it's from a neighbor who probably saw Rowena kill Miles.
- Foreshadowing: Some of Grace's playful lines to Rowena allude to the former witnessing the latter helping her mother bury her father's corpse when she was a child."Actions have consequences, Ro. You can't just forget people! Bury them and pretend like they never existed."
"Regards to your mother!"
- Frame-Up: The Twist Ending unveils that Rowena's intention to follow Harrison was to frame him for Grace's murder—presumably because there was much evidence pointing to him and since she could then write a feasible story to cover her tracks. In the film's final scene, Rowena does it again when she murders Miles and makes it seem that he admitted to killing Grace before she killed him in self-defense... but this time, a neighbor probably saw it all happen.
- Karma Houdini: Rowena's murdered at least three people and successfully framed an innocent man for one of the deaths, apparently getting away with it all. Even so, it's implied that a neighbor may have witnessed Miles' murder.
- Hired to Hunt Yourself: Rowena "investigated" Harrison for Grace's murder to hide the fact that she was her killer.
- Parental Incest: In her childhood, Rowena was sexually abused by her father, prompting her mother to kill him.
- The Killer in Me: The film somehow manages to do both. Rowena's initially presented as a reporter who's investigating the murder of Grace, with the most likely culprit being Harrison. However, it's revealed that she was Grace's killer—having done her in to end years of blackmailing before she successfully pins the blame on the innocent if slimy-looking businessman. Oh, and she resorts to murder again when Miles tries to blackmail her about setting Harrison up. All this would look like the Secretive Killer type... except that she's surprised several times by developments she should've already known, which would make her seem to be the Amnesiac Killer type. This is allegedly because the twist of Rowena being Grace's killer is the result of a last-minute change of the film's ending.
- "Ray of Hope" Ending: Rowena succeeds in murdering Miles and making it like he attacked her after revealing himself as Grace's murderer. However, the final shot is of a neighbor looking out his window, implying he saw what really happened and can tell the truth to the police.
- Shout-Out: When Bill arrives to see Rowena and Miles, the latter tells him to drop the glasses because he isn't Deep Throat.
- Stalker Shrine: Miles made one of Rowena that's hidden in a secret room in his house.
- Stalker with a Crush: Miles sneaks into Rowena's house and watches her make out with her boyfriend Cameron, tries to flirt with her online while he's impersonating Harrison, and has a freaky shrine dedicated to her in his house. Averted with Rowena since she's using her romantic charm on Harrison as part of her plan to frame him for Grace's murder.
- Too Dumb to Live: Miles finds out that Rowena murdered Grace after years of being blackmailed, so Miles decides to... try doing the same thing. Guess how well that ends.
- Undercover When Alone: Rowena is snooping around Harrison's apartment when she finds evidence that seems to indicate that he murdered Grace, which is when she becomes visibly scared. However, she was the killer all along. Apparently, it's due to how the ending was changed to make Berry's character the guilty party—all logic be damned.
- Wham Shot: Near the film's end, someone removes an incriminating vial of belladonna from a deodorant can, meaning they're the actual killer of Grace. This person closes their bathroom's cabinet, revealing them to be Rowena.