The planned a royal visit by Princess Margaret to open a new school library in Kembleford is in doubt when the library is found vandalized and lush caretaker Raymond Harrison next morning found hammer-skull-smashed. Harrison, a pickpocket who had been in prison, carried a locket with a schoolgirl photo of the current headmistress Amanda Clement, whom inspector Sullivan arrests as her fingerprints are on the murder weapon, which is found in her desk. Harrison owed money to ambitious mayor Wood, who now gets the glory to receive the princess, instead of the principal, who hopes to stand against him in the next election. Royal protection officer inspector Beckett and Royal aide Elizabeth Barnes, were also present. Father Brown is more interested in a gold lighter that Barnes had, which actually belonged to Princess Margaret, pick-pocketed from Barnes and recovered by Inspector Beckett who knew of Harrison's past. An old newspaper seen at Harrison's, now missing, yields the crucial clue for Brown, relying on Sullivan remembering a football match played in 1937 to identify the date and identify the killer.
—KGF Vissers