Puck has been invited by her tutor at the university to celebrate midsummer at his secluded cottage on an island together with a group of friends, among them Einar Bure. Puck and Einar are having a secret relationship, and he is the reason she says yes to the invitation. Having been out on a romantic spree with Einar, Puck finds one of the female guests murdered. Einar contacts his friend Christer Wijk, but upon Christer's arrival, the dead body has disappeared. The contact with the outside world is broken when the island's only boat goes missing. They are trapped on the island - and someone among them is a killer...