Quinnan and Jarvis investigate when they find a young man in possession of some lethal Class B drugs which he claims were prescribed to him for slimming. They decide to mount an undercover operation to catch a fraudulent doctor at a slimming clinic, but need a WPC for help. Dare they imply that Page or Keane are overweight? Keane goes undercover, but discovers that the doctor is interested in more than just his patients' weight.