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.