Frank and Luella are employed by Val Twigg to investigate the business model of a rival slimming company, Fatbusters, who have stolen her clients. Luella goes undercover as a client to discover the method used to induce clients to lose weight. The head of Fatbusters is the charismatic Kit Willow who used to work with Twigg and has a new business partner in Diana Winter. One of his clients is "Slim" Jim Sandford who until recently had lost a lot of weight. Another client is Luella's sister Lia and her fractious behaviour is never far away as they are clearing their mother's house approaching the anniversary of her loss at sea. The cleaner at the club also displays irrational behaviour and Frank suspects drugs. When Willow is murdered in a frenzied attack Detective Sergeant Keeler arrests Twigg as the last person to see him alive.