On a hot July morning on Sweden's idyllic vacation island of Sandhamn, a man takes his dog for a walk and makes a gruesome discovery: a body, tangled in fishing net, has washed ashore.

Police detective Thomas Andreasson is the first to arrive on the scene. Before long, he has identified the deceased as Krister Berggren, a bachelor from the mainland who has been missing for months. All signs point to an accident - until another brutalized corpse is found at the local bed-and-breakfast. But this time it is Berggren's cousin, whom Thomas interviewed in Stockholm just days before.

As the island's residents reel from the news, Thomas turns to his childhood friend, local lawyer Nora Linde. Together, they attempt to unravel the riddles left behind by these two mysterious outsiders - while trying to make sense of the difficult twists their own lives have taken since the shared summer days of their youth.