PCs Jim Carver and Des Taviner are following PC Polly Page and Terry Knowles into a flat where they find terrified tenant Billy Martin. Outside they chase two masked men but lose them. As they return, Taviner is water bombed by kids, much to his colleagues' amusement. Later, Page and Knowles spot a man hanging around a local school. Knowles gives chase but loses him. Using the computer Page identifies him as Dave Scoby, a registered sex offender. Knowles notices his address and is concerned as he lives near his sister and her daughters. Page makes it clear that no matter what his concerns are he is not allowed to tell them. Knowles struggles to keep this information to himself but unwisely confides in his mate Taviner. However, when Knowles' sister does find out, the finger of suspicion points firmly at her brother as the 'grass'.