The film follows Lars Nystrom, who dons a disguise to raid a central Stockholm bank. He then takes hostages in order to spring his pal Gunnar from prison. One of the hostages includes Bianca, a wife and mother of two. Negotiations with detectives hits a wall when (at the request of the Prime Minister) the police refuse to let Lars leave in a getaway car with the hostages.
As hours turn into days, Lars alternates between threatening the hostages and making them feel comfortable and secure. The hostages develop an uneasy relationship with their captor, which is particularly complex for Bianca, who develops a strong bond with Lars as she witnesses his caring nature. This connection gave rise to the psychological phenomenon known as "Stockholm syndrome".