When DI Ben Kitto sees a baby thrown into Penzance harbour, he prays it’s a trick of the light. But the threat is real. The child survives – barely – and soon a chilling pattern emerges.

As the Dark Sky Festival brings dancers, dreamers and stargazers to Cornwall’s coast, children begin to vanish. A small mermaid figurine is found beside each scene, echoing the legend of the Mermaid of Zennor, who lured a man to his death beneath the waves. Still reeling from a devastating bereavement and determined to protect his young son, Ben is pulled back into the field and into a deadly investigation.

When the killer’s messages begin arriving at his home, the threat becomes terrifyingly personal. Suspicions fall on familiar faces. When the summer solstice approaches, Ben must confront the boundaries of love, loss and obsession.

In a final, desperate chase along the headland, only his bond with Noah – and the loyalty of his dog, Shadow – can prevent tragedy from repeating itself.