Iceland, 1956. Fourteen-year-old Lára decides to spend the summer working for a couple on the small island of Videy, just off the coast of Reykjavík. In early August, the girl disappears without a trace. Time passes, and the mystery becomes Iceland's most infamous unsolved case. What happened to the young girl? Is she still alive? Did she leave the island, or did something happen to her there?

Thirty years later, as the city of Reykjavík celebrates its 200th anniversary, journalist Valur Robertsson begins his own investigation into Lára's case. But as he draws closer to discovering the secret, and with the eyes of Reykjavík upon him, it soon becomes clear that Lára's disappearance is a mystery that someone will stop at nothing to keep unsolved . . .