Father Brown, Sergeant Goodfellow, Inspector Mallory and his family receive an invite for the 20th anniversary of Chummy's holiday camp. During the visit, owner Marjorie Chummy is strangled with an apron belonging to Mavis Jug, maid and general dogsbody at the camp. Inspector Mallory arrests her while Father Brown and Sergeant Goodfellow look at the other staff, Jock McCudgeon, Griff Grimshaw, and Sandy Beauchamp, at the camp who Mrs Chummy kept under a tight rein. Father Brown discovers a child, Billy Fairfield, had died in the past in the camp swimming pool that Mavis Jug, then an "Orangecoat", and Mrs Chummy should have been supervising.