A female serial killer with a deadly agenda. The detective who must stop her. Luxury holiday lodges in the stunning Peak District. The game begins . . .Callum is lured to an isolated boathouse by an attractive older woman. When she gets him alone, she knocks him out with a single blow. As he wakes up, her voice comes out of the darkness, "You're a sprat to catch a mackerel".Surrounded by hills and lakes, Still Waters is home to a close-knit community of wealthy retirees. It's an unlikely setting for violence. The police don't take Callum's disappearance seriously: he's 24-years-old, after all. But Callum's mother, a Still Waters resident, knows that something is very wrong.Then a body is discovered floating in the lake. Head bashed in. But it's not Callum.And someone tweets: Come out to play one last time, Alice. Still Waters run deep. #MadHatter.That's when DCI Alice Rossi is called in. She's back.