Every morning and evening, Zoe Walker takes the same route to the train station, waits at a certain place on the platform, finds her favorite spot in the car, never suspecting that someone is watching her. It all starts with a classified ad. During her commute home one night, while glancing through her local paper, Zoe sees her own face staring back at her - a grainy photo along with a phone number and a listing for a website called FindTheOne.com. Other women begin appearing in the same ad, a different one every day, and Zoe realizes they've become the victims of increasingly violent crimes - including murder. With the help of a determined cop, she uncovers the ad's twisted purpose, a discovery that turns her paranoia into full-blown panic. Zoe is sure that someone close to her has set her up as the next target. And now that man on the train - the one smiling at Zoe from across the car - could be more than just a friendly stranger. He could be someone who has deliberately chosen her and is ready to make his next move.