Professor Ambrose is abducted after sending his friend Father Brown an ancient prayer book which supposedly can locate the long disappeared Lannington rosary, said to hold healing powers. Aided by Lady Felicia's chauffeur Sid the priest uses the book to find clues which will lead him to the rosary. There is a deadline as a ransom note arrives, informing the father that the rosary must be delivered to save his friend's life whilst the quest is complicated by the arrival of supposedly reformed criminal Flambeau, who claims he is working as a mercenary for the Papacy to find the relic. And then there is a third party, the actual kidnapper, whom Father Brown must expose.

Farmer John Tatton and his son Alfred do not get on, John accusing the boy of being a useless drunk like his late mother. Alfred confronts the family doctor Adam Crawford, taunting him for having a much younger wife Oona, who has just confided in Mrs McCarthy that she is pregnant. Alfred is found dead, mangled in farm machinery and soon afterwards anonymous letters appear, accusing Dr Crawford of the crime as Oona was supposedly having an affair with the dead man - something she denies. Dr Crawford confesses to the murder of Alfred but Father Brown knows better and seeks out the truth.

Audrey McMurray, a rally driver and property owner, may appear to be a philanthropist but her ruthless treatment of her tenants has caused Harriet Welsby's husband to kill himself whilst she openly cheats on her husband Walter with young mechanic Gary Bakewell. Audrey is killed in a hill climb after somebody tampers with her car's brakes and Harriet is arrested after threatening her. Then Gary confesses but Father Brown is convinced that Walter and his wife's secretary Phyllis, who are lovers, are the culprits though he has difficulty in persuading Sullivan to let him ensure that justice is done.

Father Brown investigates the murder of a former hangman.

Father Brown must help Flambeau in stealing the Pope's gift to the Queen.

When Robert Twyman receives a note telling him to "confess" or his son will die and the threat is carried out, Father Brown must figure out how the killer got into and out of a securely locked house.