A passionate holiday romance leads to an obsessive relationship when an Australian photojournalist wakes one morning in a Berlin apartment and is unable to leave.
Clare (Teresa Palmer), a young Australian backpacker, is exploring Berlin when she meets a local man named Andi (Max Riemelt) and has a one-night stand with him. The next morning, however, she finds that he has locked her in his apartment. Clare believes Andi when he says he accidentally forgot to leave her a key, and she stays with him another night. Soon, however, Clare realises Andi has no intention of ever letting her go, discovering that he has written the word meine (mine) on her shoulder and stolen her SIM card from her phone. Clare tries to escape by smashing the windows but discovers they are double paned. To her amazement, when Andi comes home, he acts like nothing is wrong, offering her flowers and pesto. She attacks him but he physically restrains her, then keeps her tied up.
While Clare is confined to his apartment, Andi goes to dinner with his father, a professor, and mentions that he’s dating a new woman. Andi’s father asks what happened to Natalie, and Andi tells him that she went back to Canada. His father mentions Andi’s mother, prompting Andi to speak bitterly about how she defected to the west before the Wall came down. That night, when Andi lets Clare shower, she is horrified to find long blond hair clumped in the drain, and realises she is probably not his first victim. Meanwhile, Andi pretends that things are normal, cheerfully telling Clare, “I told my father about us” and “I texted your mother for you.” Clare uses a screwdriver to attack Andi and flee the apartment, but he catches up with her and brings her back after breaking her hand.
One night, Franka, a student at the sports school where Andi teaches, shows up at his apartment. When Franka sees a flash of Clare in a towel, Andi tells her it’s his girlfriend and puts her down, causing her to leave. Meanwhile, Andi continues with his bizarre behaviour, taking Polaroids of Clare in disturbing positions and cutting off pieces of her hair. Some time later, Andi finds out his father has died in his sleep. A depressed Andi stays in his father’s house for a week, while Clare is left in the apartment with the power turned off. Unable to escape, she takes Polaroids of herself and eats what is left of the food until Andi finally returns. Clare, who appears to exhibit Stockholm syndrome, appears relieved as she thought he was not going to come back….