Charles Schine (Clive Owen) and Lucinda Harris (Jennifer Aniston) have noticed each other on the commuter train before. One morning their conversation leads to a flirtation which turns into an evening drink and then, before either one can stop it, a passionate one-night stand.
But suddenly a stranger explodes into their world, threatening to expose their secret and lures them into a terrifying game with more surprises then they saw coming and more danger then they may survive.
