Part one of two. When seven-year-old Mark Tildesley disappears from a Wokingham funfair in 1984, it sparks a chain of events that will uncover one of the most depraved gangs of child abusers and killers that Britain has ever seen. Featuring interviews with key police officers involved in the case, plus family members of the victims, this documentary tells the story of a prolific gang of abusers