Police detective Roland Prengler goes undercover in the small town of Ahndorf to investigate a murder case that has baffled local officials for quite some time. Three years ago, Lucy, a 17-year-old, disappeared without a trace. The police have good reason to believe she was murdered and they even have a suspect - Walter, a down-on-his-luck drunkard who lives at an abandoned farm on the outskirts of town. Roland's assignment is to befriend the eccentric outsider, gain his trust and get him to confess to the crime. But the deceptive friendship soon takes its toll on the experienced cop and puts his principles as a human being to the test.