Once you cross the wrong lines, there's no turning back.

For DS Liam Kilshaw, a former marine who almost died on a mission gone wrong, returning to the sea was meant to help combat his PTSD. But when he's called out with the lifeboat crew off the rugged Cornish coast at night, the dark danger of the waves comes crashing back. The body of a young man is floating in the water, and the zip-tie marks on his wrists show this is no tragic drowning--it's murder.

It's not the first suspicious death to shock the tight-knit community: the identical discovery of a young woman with connections to a county lines drugs gang leads Kilshaw to suspect the killings must be linked. But as the brooding Cornish coast and whispered local rumours fold darkly around him, he starts to feel he can't trust the water or anyone in town.

As the bodies keep coming, he must confront a sinister gangland underworld as well as his own demons--before tragedy strikes even closer to home.