The lighthouse at Porth Trevan has stood on its headland since 1870. The village likes to joke that it has seen everything the town ever tried to hide.

Before dawn one autumn morning, lobster fisherman Lucas Ward watches a boat with no lights slip away from the cliffs. Minutes later he pulls a woman from the water. May Hollis grew up in the village, spent most of her life somewhere else and came back only weeks ago, asking questions nobody wanted to answer.

That same morning, Emma Trelawney drives down into Porth Trevan, home for the first time in twenty years. She has lost her career, sold everything she owned in London and come home to deal with her mother’s empty cottage. She has not come home to think about her sister Anna, who went down to those same cliffs twenty years ago and was never seen again.

But May had been asking about Anna. About the caves beneath the lighthouse. About boats that came at night. And in Anna’s old bedroom, Emma finds a notebook her sister never finished, with one line she can’t stop reading: The tunnel goes deeper than anyone thinks.

Someone in Porth Trevan knows exactly what is down there. And they have already noticed that Emma is looking.