Set in Toronto, Canada, the film follows Catherine Stewart (Moore), a successful gynecologist, who is married to David (Neeson), an opera expert with the distressing habit of flirting with virtually any other woman he encounters. Meanwhile, their son becomes increasingly difficult to control, leaving Catherine feeling alienated in her own house. After David misses a birthday party, Catherine becomes especially suspicious that he is cheating on her. This leads to the very bad idea of hiring a prostitute that she had encountered earlier (Seyfried) to test David's resolve. Soon, Chloe is graphically describing her encounters with David to Catherine. But it becomes increasingly clear that David isn't the one Chloe is interested in...
The film attracted some early notice for very tragic reasons: Liam Neeson was in the middle of filming it when his wife Natasha Richardson died in a skiing accident.
This movie provides examples of:
- Adaptation Relationship Overhaul: In Nathalie, the French film that served as the basis for this one, Catherine and Nathalie's relationship never goes beyond Unresolved Sexual Tension, nor is there a mother-daughter element, nor does Nathalie go dangerously crazy for Catherine.
- All Men Are Perverts: Initially it looks like this is in full effect, but scaled back a bit as David never actually cheated; he just thought about it, a lot.
- Ascended Extra: Catherine's son is a more important character in Chloe than in Nathalie. In the French film he's just there, being well-behaved, and he doesn't sleep with Nathalie (whom he doesn't even meet). In Chloe he's played up more as a hormonal teen and is a big source of concern and stress for Catherine.
- Batman Gambit: Chloe's scheme ends as soon as Catherine decides that she is done testing her husband. Chloe has to play off of Catherine's insecurity and arousal to keep it rolling.
- Bury Your Gays: The ending for Chloe, who seems to be bisexual, when she falls from a window to her death not minutes after sharing a kiss with Catherine, and whom she previously had sex with.
- Crucified Hero Shot: Crucified villain shot, although YMMV big time over whether she's the villain.
- A Date with Rosie Palms: Implied but not explicitly shown with Catherine who is taking a long hot shower after hearing Chloe's explicit details of her trysts with David, and as she fantasizes about such, continues to move her shower head down....
- Death by Adaptation: Chloe dies at the end, whereas her French analogue Nathalie survives her film unscathed.
- Depraved Bisexual: Chloe, who it turns out is highly attracted to Catherine, not taking her rejection well at all, which turns her into a stalker. Then she even threatens to kill Catherine if she won't get together with Chloe. Possibly Catherine as well, depending on how one views her actions and relationship with Chloe.
- Driven to Suicide: Chloe kills herself due to Catherine's rejection.
- Girl-on-Girl Is Hot: Chloe seduces Catherine and they have sex in the hotel. Once he finds out, David's reaction is muted, possibly because he finds this appealing instead of threatening.
- Good Adultery, Bad Adultery: Deconstructed quite extensively. While Catherine is driven to find out about her husband's infidelities, she is, all the same, turned on by the recounting of the details. When David hears about Catherine sleeping with Chloe, he doesn't seem all that upset at all. Of course, he IS a man and men often like that sort of thing.
- Hypocrite: Catherine gets mad at David for working so late and accuses him of having affairs, despite herself committing adultery with the same woman she hired to seduce David.
- If I Can't Have You...: Chloe is so emotionally distraught by Catherine's rejection of her that she threatens to kill herself then threatens to kill Catherine with her hair pin unless she chooses to be with her.
- Love Father, Love Son: A gender-flipped version of this, with Chloe, Catherine and Catherine's son Michael. After Catherine ends her affair with Chloe so she could repair her marriage, Chloe meets then seduces Michael, Catherine and David's son in order to gain access to the inside of Catherine's house. While Michael immediately believes Chloe's actions as her having feelings for him as he does for her and even considered her his 'new girlfriend' after their tryst together, Chloe, on the other hand, only has feelings for Catherine and was willing to seduce Michael in order to get closer to his mother.
- Love Triangle: David, Catherine and Chloe, though luckily it's resolved quickly by the end. A second variety is Catherine, Chloe and Catherine's son Michael.
- Ms. Fanservice: While nudity is somewhat expected in an erotic thriller, Amanda Seyfried just can't seem to keep her clothes on here as Chloe, shown nude from the rear and side along with topless, plus in two sex scenes.
- Platonic Prostitution: Initially, Catherine pays Chloe just to meet her husband at a cafe and see if he flirts with her. Later subverted, however it turns out Chloe's lying about having sex with him.
- Relationship-Salvaging Disaster: David and Catherine, after everything they've been through, are seen embracing each other after Chloe kills herself in their house.
- Retargeted Lust: Catherine, after hearing Chloe tell explicit details about her encounters with David, she becomes aroused and experiments with herself in the shower while fantasizing about David and Chloe together. Later, Catherine asks Chloe to show her how David touches her and she seduces her. After the affair is terminated, Chloe seduces Michael but looks over at Catherine's belongings while she's in bed with him.
- The Reveal: Chloe never actually met with David, and was lying to Catherine about all of their encounters.
- Shower Scene: Catherine is shown taking a shower, where she's not only seen topless but starts using the sprayer for her stimulation.
- Spurned into Suicide: Chloe, who willingly lets go of the window she's holding onto and falls to her death after Catherine choose to save her marriage over being with Chloe.
- Stalker with a Crush: The title character.
- Television Geography: Averted. Toronto usually doubles for other cities; this time around it's playing itself. Egoyan has said that he intentionally set as many scenes at well-known Toronto landmarks as possible (seriously, if you went to the University of Toronto or work in Downtown Toronto, you've probably walked by every filming location in the movie), in reaction to all those films shot in generic Toronto locales to hide the fact that they are in Toronto.
- The Unfair Sex: If Catherine had been a man who had an affair with someone young enough to be his daughter, then push her away when she became emotionally attached and refused to take money to just go away (resulting in her suicide), he would likely be much less sympathetic than she is as a woman.
- Yandere: Chloe borders on this after Catherine ends their affair, as she soon begins to send threatening e-mails to Catherine, showing pictures of them together in bed that could jeopardize her job. Later, she begins stalking Catherine and her husband David and was willing to sleep with their teenage son just to gain access to Catherine's house and await her.