With the local lido under threat of closure by ruthless businesswoman Alison Sutherland, the Save the Salthaven Lido campaigners are fighting a desperate battle to keep it open. When the lead campaigner is discovered dead, partially drowned and stabbed repeatedly, suspicion falls upon Alison.

No sooner have DI Sarah Gilchrist and DS Bellamy Heap spoken to Alison, one of her colleagues suffers a heart attack - despite being in good health - during a long-distance, open-water swim. Hot on the heels of this, another swimmer turns up drowned.

Are all the deaths connected to the Salthaven development? Is someone targeting open-water swimmers? Gilchrist and Heap race to uncover the truth before more victims come to the surface.