Puck Ekstedt, a doctoral student in literature, is invited by his supervisor Rutger to spend the summer solstice with him and his wife at their summer home on an isolated island. When he reveals that the young historian Einar Bure will also be there, Puck gladly agrees. When he arrives at the summer solstice party on the island, he meets a group of young people, whose lives have been intertwined since their student days. He quickly becomes aware of a web of tensions between them, both erotic and harrowing. These tensions rise when Rutger's ex-fiancée, Marianne Wallman, shows up unexpectedly with his girlfriend Viveka Stensson. The next morning, Puck stumbles upon Marianne's dead body in the woods. Puck and Einar take the motorboat across the lake to call Einar's friend, Christer Wijk, head of the national homicide investigation team. When Christer reaches the island, the boat's engine breaks down. There is no other boat, no phone, so now everyone is isolated together on the island. The murderer...