Downtrodden Simon James (Jesse Eisenberg) has worked at his office for seven years, but he is ignored by his boss, named The Colonel, and colleagues. From his apartment he spies on a beautiful co-worker he admires, Hannah (Mia Wasikowska), who lives in the apartment opposite him. He sees her throwing away art and secretly retrieves and admires it. One night, Simon sees a man jump to his death from the floor above Hannah's apartment. He talks to detectives, who explain that if the man had jumped a few feet to the right, he would have been badly hurt but would have survived.Simon's boss (Wallace Shawn) announces the arrival of a new employee, James Simon (also played by Eisenberg), who looks identical to Simon, which causes Simon to faint upon first glance. Assertive and charming, James is Simon's polar opposite. Much to Simon's annoyance, James not only gets respect from their co-workers but no one seems to notice that they are identical in appearance. James, on the other hand, does notice this and sees Simon's pain. Out of pity, he decides to buddy-up with Simon and give him advice about how to seduce Hannah. Hannah then asks James on a date through Simon. On the date, Simon pretends to be James, with the real James giving him instructions via earpiece. When Simon becomes nervous, the two swap places and James kisses Hannah, angering Simon. James asks Simon to take an aptitude test in his place and seduces their boss's surly, rebellious daughter, Melanie (Yasmin Paige), whom Simon was reluctantly hired to tutor.Simon gets his revenge on James by revealing to Hannah that James is cheating on her with Melanie. Furious, James blackmails Simon for his apartment keys using explicit photos he took of himself with Melanie, knowing their boss will believe it is Simon in the photos. At work, Simon accuses James of being an imposter and is fired after going on a maniacal tirade. As he is about to kill himself, he sees Hannah lying unconscious in her apartment. He calls an ambulance and accompanies her to the hospital, where it is revealed that she not only overdosed but also miscarried (she had become pregnant after a sexual encounter with James). Simon then takes Hannah back home, relieved that she has survived. Still upset, however, Hannah states that she wanted to die and she suggests that Simon kill himself. She goes through Simon's jacket pockets and discovers earrings he had bought for her and her salvaged art.Simon learns his mother has died and finds James at her funeral. Simon punches him and discovers that they share injuries; as James's nose bleeds, so does Simon's. He finds Hannah and tells her he wants to be noticed. He goes to his apartment and handcuffs the sleeping James to his bed, then goes to the ledge above Hannah's apartment, steps to the right, and jumps. He is badly hurt. Hannah runs to him and an ambulance arrives. Lacking medical attention, the handcuffed James appears to be on the brink of death as he lies motionless on the apartment floor.Inside the ambulance, The Colonel (James Fox) and Hannah watch over Simon. The Colonel tells Simon that he is "special", to which the latter responds with a half-smile, "I'd like to think I'm pretty unique".