Father Brown (Mark Williams) welcomes Aldous (Richard Huw) and his daughter Grace (Pepter Lunkuse) to Kembleford, who are visiting for the County Fair. They've recently moved from Tanganyika and are on the lookout for a medical school for Grace. Excited about the antiques marquee, Mrs McCarthy (Sorcha Cusack) can't wait to have her heirloom broach valued. At the Red Lion, Bunty (Emer Kenny) offers a room at Montague to antiques expert Wynford (Miles Jupp) who isn't happy with the accommodation at the inn. The next morning Grace finds her father's body the floor of his room. As Father Brown comforts her, Inspector Mallory (Jack Deam) arrests Grace, accusing her of giving her father sleeping pills that interfered with his malaria medication, after she found out that he could no longer fund her education. Father Brown however believes Grace's grief is genuine and is determined to find the real culprit...