As Father Brown (Mark Williams) approaches Kembleford's mobile library, Ada (Holly Bodimeade) emerges to ask for help. Margaret (Elizabeth Berrington) lies under a pile of books, pinned beneath a metal shelving unit. Father Brown is relieved to find that she's still alive. With Margaret now safe in bed, Mrs McCarthy (Sorcha Cusack) insists that she help in the mobile library until Margaret's better. Her husband Graham (Andrew Greenough) shows them out through his photography shop, bumping into his scruffy assistant Lewis (Thomas Pickles). Later Lewis tells Father Brown that he has a secret in the confessional, before running out. That night Graham and Margaret are woken by crashing below. Downstairs, Graham swings a cricket bat in the dark and it connects with a sickening thud. When he turns the lights on, Lewis lies at his feet, dead. Inspector Mallory (Jack Deam) believes it's reasonable self-defence but Father Brown suspects it's not quite that simple...