Father Brown's investigation concludes God's law is above man's law. Bunty and Mrs McCarthy are not convinced of the behaviour of Hardwick's widow and both believe that he is still alive. He invites Father Brown and Mrs McCarthy, a fan of Bishop, to view the filming. A fourth series of ten episodes was commissioned in 2015. The mother, recently released from prison, is arrested and a motive for Lee's wife emerges.
Laura's boyfriend, the clown's girlfriend, and another clown are all suspected. Father Brown uncovers years of bullying at the school and the use of a modified cat o' nine tails. Mallory arrests neighbour Hermione Harvey who had a revolver and hated Reeve. Esta is created by Rachel Flowerday EastEnders with Tahsin Guner Casualty. Father Brown discovers a deadly pact involving a child abuse victim and the murdered man's wife to kill another man while providing unbreakable alibis.
The suicide and a note left by another lover of Fitzgerald complicates the issue as he had been sacked by her husband when he caught them kissing. Events take an unusual turn when he returns to life two days later at his church committal. Lady Felicia has to choose between lover and husband and Moscow get the film they do not expect. When the maid Ruby is found dead, Lady Felicia's niece, Bunty, is suspected. The truth of a father in debt leads Father Brown to another conclusion about the deaths. The three cast members and new producer, who falls for Bunty and wants to impress, are suspected.
When Alfred is killed in a threshing machine, the doctor is suspected when accusatory appear. She has lured a town councillor into a compromising position so Nelson can obtain a boxing venue. A plan that begins to unravel when Flambeau's victim fails to reappear after he is murdered by his wife intent on obtaining the gold medallion for herself. The bidders soon arrive: an army major, a clairvoyant and her son, and a collector of objets d'art. Father Brown suspects the answer lies at the end of a Labyrinth and a sad secret the Malmorts are hiding. Sullivan enlisting Father Brown's help capture Tylett who protests his innocence. Jealousy among the followers leads to murder, in a locked room, of Kalon's wife.
One of the photographs is of Ada. There is something in the prison he wants, something valuable. Bent on revenge, Sid confronts his defence lawyer Giles Foster, now a judge, with Father Brown at the home of a Edward Reese who appointed Foster. Father Brown enlists Sid to go undercover as a trainee priest despite Mrs McCarthy's misgivings. However, his skills and links to the criminal underworld of Kembleford are often needed to solve a case. Lewis was apparently taking pornographic pictures of young women and furthermore he had been poisoned and his body dumped at the Cartwrights before Graham hit him.
The Chesterton stories were set all over the world and at different times, but a decision was made to anchor the stories in a fixed place and time. His commitment to obeying the often presents unique circumstances. Bunty finds the show announcer's diary revealing his colourful lifestyle and his new found prospects. As the only key-holder, the manager is arrested by Inspector Sullivan. Father Brown is drawn into the shady world of London Boxing promoter and racketeer, Denis Nelson, who is involved in illegal betting, fixed fights, and blackmail.
Whittaker is a ruthless agent who blackmails Lady Felicia. The prospective closure of the local railway station leads to a fund raising event to save it, at which the station master Ben Webb is found murdered. Inspector Mallory allows the contest to continue when a gunshot is heard and Reeve is found shot dead in his study. The victim is a business associate of Flambeau, Flynn Hardwick despite protesting his innocence, he pleads guilty to his murder and is sentenced to hang. Fox is part of the Diocese and reports to Bishop Reynard.
Sid Carter brings letters for Father Brown and Bunty as well as a Christmas present for Mrs McCarthy. A second murder occurs, with the Father's dangerous conclusion that the murderer is one of the remaining guests. The reality is that actor Alex Price has been busy in the theatre to do the new series. During a golf tournament he is murdered but there is another corpse, that of a man Reeve's daughter Tamara clearly recognizes. When Foster is found dead from stabbing by a glass to the throat, Sid is accused by Reese's son of the murder.
Father Brown meets a visiting German priest, arousing hostility amongst the villagers with recent war memories. Brown lives in Kembleford, an English fictional town where help local police solve crimes that happen around. When her husband's finger turns up in a pig's stomach, it points to a serial killer amongst the family. When their landlady is murdered by smoke from a blocked chimney, yet her three kittens survived. Chief suspect is Deepak Chatterjee, the man in charge of rail closure, but he reveals a secret about Ben which allows Father Brown to unmask the real killer, in addition to acting as an impromptu midwife.