Ellie Pentreath has spent half her life avoiding the sea. When her radio career collapses after she reports a voice no one else believes is there, she returns to the Isles of Scilly expecting an inheritance she can refuse. Instead, a dead musician has left her a lighthouse. There are conditions. Ellie must live there immediately. She must make the light viable. And before midsummer, she must satisfy the Council officer determined to take it from her. 

The lighthouse should be empty. But inside it Ellie finds scorched rope, impossible wreck records, a child's drawing of herself, warm glass with no power, and a lullaby caught in radio static. As her sister, niece, first love and the dead man's son are drawn into the tower's mystery, Ellie discovers the failing beam is not simply a light. And the puffins that vanished from the headland thirty years ago may have been the first to know something had gone wrong.