Few things are as compelling as a good twist ending, the kind that invites reconsideration of everything that came before it. Problem is, it's devilishly hard to play fair with an audience on a twist-ending story, because films often make the big secret either too obvious, or so improbable that it seems like a cheat. The thriller Perfect Stranger falls squarely in the latter camp, while also inventing its own special problem: By the time the reveal snaps the loose ends into place, the question "Why is any of this idiocy happening?" has been looming oppressively over the film for so long that no answer could possibly seem satisfying.
As the film opens, unlikely super-journalist Halle Berry and her partner, tech wizard Giovanni Ribisi, are completing an exposé on a Mark Foley-esque page-schtuppin' politician, but their newspaper cancels their story, sending Berry into an unconvincing apoplectic rage. She promptly quits her job, which leaves her with a lot of free time for dealing with the out-of-nowhere demands of her estranged childhood friend Nicki Aycox, who materializes in a subway station and demands help in blackmailing her lover, super-rich ad-man Bruce Willis. Berry doesn't show much interest until Aycox turns up murdered. Then Berry launches a thoroughly standard tech-thriller investigation, infiltrating Willis' ad company under a false ID, sneering over erotic online chats with him, hacking into his computer, and so forth.
Meanwhile, Ribisi has an unhealthy crush on Berry, Berry has an on-again-off-again relationship with a boyfriend who cheated on her with Aycox, Aycox was pregnant and the child could be anyone's, Willis has a statuesque lesbian minder and a gorgeous wife who's stalking him, and something presumably important is going on with Berry's savage nightmares and flashbacks to little girls in the snow. Screenwriter Todd Komarnicki piles on the subplots (and the clumsy recaps and exposition) as if trying to keep viewers too dizzy to think things through, not that anything about the film actually invites much thought. Berry's unpleasant character makes a lousy hook; she spends half the film ordering Ribisi around and ignoring him when she doesn't need his help, and the other half sitting at computers, reading her own text messages and emails out loud. When the left-field ending finally arrives, it explains a lot, including why she's so off-putting and histrionic, but it never really explains why audiences should bother sitting through such a tangled mess.