Puck receives an invitation from her university tutor to join a midsummer celebration at his remote cottage on an island, along with several friends, including Einar Bure. Puck and Einar are secretly involved, which motivates her to accept the invitation. During a romantic outing with Einar, Puck discovers that one of the female guests has been murdered. Einar reaches out to his friend Christer Wijk for help, but when Christer arrives, the corpse has vanished. Their connection to the mainland is severed when the island’s sole boat disappears, leaving them stranded with a murderer among them.