The Laws of Motion

Charlotte McKinley asks Father Brown to exorcise her house, which she believes is haunted by the ghost of her sister Elspeth, who disappeared nine years earlier. The priest believes somebody is fabricating a ghost but then Charlotte disappears from a locked room. Inspector Valentine suspects Charlotte's husband Victor, a former doctor struck off for irresponsible prescription and previously believed to have killed Elspeth. A skeleton is unearthed but it is not Elspeth's and a coded message in a book leads Father Brown to discover the fates of both sisters along with the legend of the family's hidden treasure.

Wearing only a hospital gown Felix Underwood returns to the village and says 'Murder' before collapsing, apparently dead. At his funeral however the 'corpse' comes back to life but with a loss of memory. He was a patient at Danvers Retreat, a psychiatric hospital for service personnel, which Father Brown visits, along with new Inspector Sullivan, discovering a body hidden in a well. Father Brown gets himself admitted to Danvers Retreat in order to get close to a young woman who supplies clues in biblical texts and to solve both the murder and the mystery surrounding young patient Jeremy.

When a guide is struck by an arrow at the grand opening of Pryde Castle, Father Brown is convinced that the motives lie buried in the family's past.

Violet Fernsley is due to hang for killing her violent husband Ivan but Father Brown believes in her innocence. The Fernsley family close ranks but the priest is puzzled by the fact that Polish farm-hand Piotr Symanski disappeared around the time of the murder and also seems to have been slain. Ivan's brothers' squabbling over possession of his farm seems to incriminate one or both whilst Sullivan is suspicious of the fact that prison warder Charlie Denham is Violet's lover. Father Brown naturally deduces that the real murderer is the least likely suspect.

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.

The father is laid up with a broken leg, strait-laced young Father Roland standing in for him. When unpopular village gossip Mrs Bunyon is killed after a row at a cake baking contest Mrs McCarthy and Lady Felicia gather evidence for Father Brown to unmask the murderer - who has also killed MRs Bunyon's baking rival Vera Thimble. Many years earlier both women gave evidence which led to the hanging of a man accused of murdering a young child. Father Brown draws the connection and tries to save a third witness from becoming the next victim.

Alice Armstrong is receiving electric shock treatment for memory loss after her accidental shooting her mother. Six weeks after her mother's death her father Sir Aaron is also found dead from a blow to the head, his hands tied. Suspicion falls on Jim Magnus, the chauffeur and a former petty crook and on Peter Royce, the secretary, who loves Alice and was sacked after telling Sir Aaron not to send her back to hospital. But a conversation with debt collector Eddie Monk informs Father Brown that the dead man owed huge sums of money and another confession suggests that Sir Aaron tied his own hands. With the death solved Alice then recollects that she was not responsible for her mother's slaying.

Ex-colonel Gerard is poisoned after arguing with his nephew Edward. Edward is a former POW from Korea and the colonel claims he has been brain-washed but Edward sticks to his story that Gerard killed his father in order to marry his widow Ada. None of the household - including Ada's brother Rupert and his adopted daughter Jia-Li - seem upset at the colonel's death and each had a motive for murder. Then Father Brown is poisoned - hopefully he can recover in time to unmask the killer.

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.