Accidental Innuendo: The Red Moon of Meru features a doctor peddling phrenology, the then-popular, now long-discredited practice of measuring intelligence by the curves of a person's head. He walks up to a fashionable lady and offers to "feel her bumps".
Anvilicious: Father Brown is a priest, so he does quite a lot of sermonizing and moralizing, giving out uplifting speeches and sometimes a few denunciatory ones. Some stand strong today, while others tend to be a victim of Values Dissonance.
Ass Pull: Chesterton was sometimes more interested in coming up with a fascinating idea for how a crime might be staged than working it into a satisfying narrative, with the end result that a couple of cases either don't do a great job of foreshadowing The Reveal or over-egg the pudding, as the British say.
Fair for Its Day: While a lot of the portrayal of Eastern religion is deeply uncomfortable, in "The Dagger With Wings" Father Brown says "It may not be like that in its real religious origins", and that his problem is with Westerners who adopt it, possibly without fully understanding it. He also says you get good and bad people in all religions.
Fridge Logic: In the first story, when Flambeau asks for the package, he reveals that he actually swiped it some time ago in the next sentence. Why would he then stay with Father Brown and ask for it at all? It's possible that, being a Gentleman Thief and all, he simply wanted to enjoy The Reveal and mock the celibate dreaming simpleton Father Brown by outsmarting him. It would be out of character; for example, at one point he lists various types of people that can be profitably robbed or swindled, along with the appropriate setting for the crime in each case.
Genius Bonus: If you want to solve the mystery of "The Actor and the Alibi" ahead of Father Brown, detailed knowledge of The School for Scandal would serve you good.
Harsher in Hindsight: In "The Honour of Israel Gow", a horrific incident of grave desecration turns out to have an innocent explanation. (A Literal-Minded and somewhat obsessive character who had been bequeathed all the gold in the deceased's possession realised after the funeral that he had forgotten about the dead man's gold tooth crown.) During the Holocaust, the Nazis would become notorious for going to similar lengths to plunder their victims' wealth.
Magnificent Bastard: M. Hercule Flambeau is an archcriminal and master thief, who is well known for being a Master of Disguise. First introduced in The Blue Cross, Flambeau befuddles the police to sneak into a convention of priests, disguising himself as one to steal a holy artifact. Only stopped by the genius of Father Brown, Flambeau accepts his defeat with grace and style but returns many times to pull off new brilliant heists until he ends up becoming a brilliant detective in his own right.
Spoiled by the Format: The first mystery, "The Blue Cross", is told through the Sympathetic P.O.V. of the great French detective, Valentin. So when the unremarkable, seemingly bumbling priest (who isn't even named Father Brown until near the end) solves the mystery, it would've been a huge shock to readers when it was first published in a magazine. But the most likely place for a modern reader to pick up this story isn't titled The Complete Detective Valentin Stories, so it ain't that much of a surprise.
Strangled by the Red String: Flambeau is mentioned to have "casually and almost abruptly fallen in love with a Spanish Lady".
They Wasted a Perfectly Good Character: The Decoy Protagonist of the very first story, Detective Valentin, had great potential as an interesting Foil to Father Brown, but the second story takes him out of the picture pretty permanently by not only having him commit the murder but follow it up with suicide when it looks like he'll be caught. To add insult to injury, the whole thing comes almost completely out of nowhere; Valentin was established to be an atheist in the first story but nothing in either tale suggests he's enough of a fanatic to murder a Catholic priest out of sheer misplaced hatred of the Church.
Values Dissonance: Chesterton's racial and national attitudes were actually very moderate for the early twentieth century, but some will often strike a sour note for modern readers in the midst of his most enjoyable works, as for example in "The God of the Gongs." His religious views, on the other hand, were entirely conscious, and will strike the reader as either refreshingly forthright or offensively aggressive, according to taste. An article published at the Golden Age of Detective Fiction Forum, The Sins of the Saint: Racism in GK Chesterton, written by a Chesterton fan, analyzes 15 Father Brown tales that seem to contain offensive content, absolving some, but not all of it. It also points that a lot of classic authors of Detective Literature (Agatha Christie, McDonald, Burton Stevenson) also had racist views, and he asks the reader to take in mind the purpose of the work (they were not racist propaganda).
The TV series
Alternative Character Interpretation: Is Mallory the least competent of the show's three inspectors, or the most self-aware? Valentine and Sullivan have cool, professional demeanors, but their self-confidence tends to make them into impenetrable stone walls of bureaucracy where Father Brown is concerned. Mallory wears his insecurities on his sleeve, but as a result, he seems paradoxically more inclined to internalize Father Brown's advice than the other two.
Fan perception of Inspector Mallory is fairly split, with just as many viewers viewing him as a truly insufferable jerk and hating him for replacing Inspector Sullivan as thinking Mallory a brilliant but lazy, amusing and lovable jerk.
A notable number of fans regard Mrs. Devine as OTT, grating—and near-unwatchable. For a character presented as being adorably quirky, a promising amateur sleuth, and caring towards others, she's proven she is none of those things over the course of only one season. (Indeed, she actually got worse throughout, not better.) Her reckless, ill-considered detecting almost sank two critical investigations—and put everyone in unnecessary danger. As well, her unbelievable romance with Chief Inspector Sullivan and her generally insipid, self-centered behavior have made many see her as more a liability than anything else.
"Blind Idiot" Translation: In The Owl of Minerva, a victim's dying words are the nonsensical "Helmet two." Later, Father Brown discovers the victim was a Franco-Brit and his actual last words were "Elle m'a tue" (pronounced ell mah too), meaning "She killed me." Except that the real French translation would be "Elle m'a tué" (pronounced ell mah too-ay). Fluent speakers such as Father Brown and the victim would never make such an elementary mistake.
Complete Monster: Father Brown himself, in his long career as a Amateur Sleuth, has encountered many killers and criminals. While the vast majority have been sympathetic individuals he managed to save, there have been some horrible exceptions:
"The Shadow Of The Scaffold": Ethel Fernsley, despite seemingly a harmless, grieving old woman, is truthfully a sociopathic attention seeker with one of the highest body counts of any killer. Faking being wheelchair bound solely to ensure she was constantly the centre of attention and could control others, for years Ethel murdered any of her farm's seasonal labourers who saw too much or threatened her facade—suffocating them by blocking the flue tube in the barn where they sleep and then feeding their bodies to her pigs. Working her daughter-in-law Violet like a slave, Ethel encouraged her vicious son Ivan's abuse of Violet—including him beating her into a miscarriage—and murdered the kind-hearted Piotr for trying to rescue Violet. Following her son Wilfred, who had discovered her method of murder, Ethel ran him over with the farm truck, crushing him to death. Finally caught, Ethel trapped Father Brown and Sid inside the barn to be devoured alive by the pigs.
"The Lair of the Libertines": Ana Demiachia is a self-described "hedonistic existentialist" obsessed with killing. Loving murder even as a child, Ana was previously a big game hunter before deciding to go after humans as her prey. Taking on the identity of Madame Chania, she lured her victims to a hotel, also being a physically abusive lover to her loyal maid Mimi. Throughout the stay of Father Brown, his friends, and some wealthy playboys, Ana kills a prostitute; leaves another one hospitalized after shooting her; tries to blow up Mrs. McCarthy and Lady Felicia; modifies one of her guests' guns to backfire and shoot him; shoots another with a crossbow; and kills the last guest before stringing him up as a twisted trophy, framing Mimi and leaving her lover to hang for her crimes. When Father Brown confronts her, Ana reveals her sadistic joy in the death she caused under her power after drugging him, before deciding to hunt him down while taunting him, ultimately falling victim to her own trap. A sociopathic, abusive hedonist who sees humans as mere animals, Ana left a body count almost never surpassed in the show, with Father Brown giving up on redeeming her.
"The Mask of the Demon": Vivian Wolsey, the head of Cardinal Pictures, while seeming just a smug and easily annoyed man is truthfully an abusive, petty predator, Control Freak, and voyeur. Constantly abusing and berating his staff throughout production, Wolsey blackmails Rex Bishop into being his leading man by threatening to expose his homosexuality and get him arrested, with Wolsey going out of way to make the experience all the more unpleasant for Bishop, simply because Bishop previously dismissed his films. The "King of the Casting Couch", Wolsey forces any woman who wants to be the lead in his films to sleep with him, while forcing himself on any who do not agree. Filming his rapes, Wolsey keeps them both for personal pleasure and blackmail material. Years earlier, when 17-year-old Bebe Fountain successfully resisted him, Wolsey, now obsessed with possessing her, subjected Bebe to a campaign of harassment and threats until she was worn down into marrying him. Wosley regularly abused Bebe throughout their marriage, while continuing to prey upon other women until his demise.
"The Eagle and the Daw" & "The Jackdaw's Revenge": Katherine Corven is a cold and calculating sociopath with an enjoyment for manipulating others. Arrested for poisoning her husband, Katherine manipulates her lover Raymond Worrall into suicide to frame Father Brown and have him executed. In her second appearance, Katherine threatens Vivian Hope to take the fall for her crimes by threatening her grandchildren. Katherine then plays sadistic mind games against Father Brown, killing a woman who had been a part of her imprisonment and attempting to incriminate Father Brown as the one responsible for her false imprisonment. Kidnapping Brown's close friend Bunty, Katherine orchestrates a setup where he would have to shoot her to save Bunty's life although secretly plotting to disguise Bunty as herself to make Father Brown shoot the wrong person and to have the priest arrested for the murder of his friend. Refusing to repent even when dying, Katherine's smug sadism reflects the darkness of her heart.
"The Devil You Know": Christina Worcester, real name Gerda Frick, was a guard in the Auschwitz concentration camp, responsible for the deaths of thousands, including women, children, the sick, and the infirm. When the Soviets arrived to liberate the camp, she took on the guise of a prisoner through a tattoo, also getting on with Eric, a forcefully conscripted Nazi, as her husband and taking on fake names in England. When Alec Frobisher tracked Gerda down and prepared to arrest her, she garroted him, and framed her husband for her crimes before murdering him and trying to escape. When Father Brown realizes the truth, Gerda holds him and Inspector Mallory at gunpoint and has them dig their graves. Father Brown's attempts to reason with her prove fruitless, as she fanatically believes that the Nazi cause was a just one, ranting about how the victor is the judge and the loser the accused. When they try to escape, Gerda catches up with them and attempts to execute them as she pulls a Redemption Rejection before dying. One of the few villains to earn Father Brown's complete contempt, Gerda was a fanatical, murderous Nazi who'd do anything and kill anyone to keep herself safe and escape justice.
"The Enigma of Antigonish": Finbar Finch is a petty, vindictive, egotistic sociopath who, four years previously, rewarded Elsie Peter's generosity in hiring him despite his lengthy criminal record by beating her senseless while robbing her, leaving Elsie disabled, traumatized, and suffering from daily seizures. Imprisoned for the assault, Finch vowed to kill everyone who testified against him. Faking repentance upon release, Finch faked his own death by fatally shooting the face off an innocent man with a shotgun, leaving false evidence at the scene to incriminate Elsie's sister Lola, ensuring she would hang. Exploiting Elsie's husband's allergies, Finch almost caused him to suffocate. Finally going after Elsie, when interrupted by Father Brown, Mrs. McCarthy, and Sid, Finch locked all four of them in a sauna to slowly cook them to death. Completely aware of his evil nature and flat-out admitting to hurting people simply for his enjoyment, even as he was dragged away by the police, Finch still vowed he would murder them all.
Harsher in Hindsight: The season one episode, The Man in the Tree comes across as this with the revelation that Sid has spent a year in jail in series 5.
Hilarious in Hindsight: Before he was Father Brown, Mark Williams played Arthur Weasley in the Harry Potter movie series. Alex Price who plays Sid Carter, left the show to be Draco Malfoy in "Harry Potter and the Cursed Child".
Moral Event Horizon: The staff of St. Bridgit's Moral Welfare, featured in "The Bride of Christ", cross it through their stealing babies from their mothers over any moral deformity, and they even had at least some of said mothers locked up in insane asylums, effectively scarring them for seven life terms. Worse, the murders of the week took place because of it—the murderer of the week happened to be one of their victims. It's telling that even Father Brown thought the whole operation was morally reprehensible, well beyond anything he had ever encountered as an amateur sleuth.
Narm: The second death in "The Crackpot of the Empire". Not only is the freight elevator's fatal plunge shown using comically-overcranked footage, but the TIE-fighter noise is used for the victim's dying scream.
Nightmare Fuel: Some of the murders in the show are creepier and more grisly than others. Special shout out to:
The Shadow of the Scaffold where the viewer sees half-eaten body parts in the pig trough.
The Smallest of Things: Agnes talking and singing in her dead sister's little girl voice when entering into a murderous fugue state, not to mention the requisite creepy dolls in her crime scene dioramas
They Wasted a Perfectly Good Plot: Kind of inevitable given that only five of Chesterton's actual stories were adapted and plenty of others that could have been included or reworked were passed over.
, written by a Chesterton fan, analyzes 15 Father Brown tales that seem to contain offensive content, absolving some, but not all of it. It also points that a lot of classic authors of Detective Literature (Agatha Christie, McDonald, Burton Stevenson) also had racist views, and he asks the reader to take in mind the purpose of the work (they were not racist propaganda).