The eleventh season finale of "Father Brown" unfolds with a nostalgic glimpse back to Valentine's Day in 1941, the 14th of February. In the heart of the Devine household, Isabel Devine (portrayed by Claudie Blakely) and her youthful family assemble in the kitchen, their attention riveted on the grave wartime updates emanating from the radio. With a quiver in her voice, Isabel voices her apprehension that the omnipresent shadow of war might encroach upon the tranquility of Kembleford by nightfall, just as her gallant husband, Ronald Devine (Darren Seed), sets forth to contribute to the war effort.
Switching to the contemporary timeline, Father Brown (Mark Williams in his iconic role) finds himself amidst the jubilant festivities organized for the Home Guard Bomb Disposal Division. Captain Fred Howton (played by Andrew Scarborough) makes a grand entrance, boasting about the unit's remarkable successes and crediting much of it to the bravery of Ronald Devine. However, the festive ambiance takes a sudden turn as the uninvited presence of Oscar Treadwell (Russell Layton), a vocal pacifist, stirs up a hornet's nest of争议. Inspector Sullivan (Tom Chambers) finds himself caught in the crossfire of this escalating dispute.
As the day progresses, Father Brown and Brenda Palmer (Rubén-May Martinwood) find themselves in awe, examining an exhibit showcasing the latest in bomb-detection technology, marveling at the ingenuity designed to combat the relentless menace of war.Father Brown's gaze swiftly alights upon Treadwell, whose discourse on the unwelcome reception of his pacifist views captivates the room. He alleges that his recent employment terminated abruptly upon his employer's discovery of his stance against the war. As the sound of target practice echoes outside, Mrs. Devine eagerly extols Sergeant Goodfellow (John Burton) and Brenda about Eddie Divine's (Barney Wilkinson) triumph in a national competition, only for Eddie to hastily rectify her, clarifying that while he did participate, he secured a commendable 4th place. The limelight then shifts to Mrs. Waterson, who exhibits remarkable marksmanship. Brenda enlightens the gathering about Mrs. Waterson's deaf son, Adam (Zaiden Raphael), who vanished six months prior to her husband's plane being shot down over Germany. A young admirer emerges in Private John Carlton (Alexander Cobb), who praises Mrs. Waterson's shooting prowess.
An uneasy encounter unfolds between Devine and Sullivan when she abruptly halts a phone call and, for reasons unknown, cancels their lunch arrangements with Eddie. Outdoors, Howton exacerbates John's already crumbling conversation with Mrs. Waterson by insisting that his ineptitude with women mirrors his clumsiness at drill. Mrs. Waterson, visibly disgusted, storms away after Howton remarks that he can scarcely fault John for pursuing "the most radiant being in Kembleford," a term of endearment for Mrs. Waterson. Though indoors and oblivious to their words, Father Brown bears witness to the awkward exchange. He continues to observe John as he approaches Eddie at the bar, confiding something in hushed tones.The revelation unfolds with stark clarity as John inadvertently discloses details pertaining to Ronald’s demise during Eddie’s highly public confrontation with him. Eddie, seething with rage, brands him a coward and even attempts a blow before Sullivan intervenes. As Eddie storms away in a fury, his parting shot rings out, “You’ll pay for this, Howton!” The next morning, Howton’s lifeless body is discovered, a single gunshot wound to the back of his head telling a grim tale. The evidence at the scene points unmistakably to an Enfield Rifle fired from a distance of 64 yards.
Goodfellow swiftly joins the investigation, confirming that Howton was staying at a nearby guesthouse, mere moments away from the scene, and revealing that an Enfield Rifle is missing from the Hall’s inventory. Despite Eddie’s vehement protests of innocence, he finds himself on the lam when Father Brown and Sullivan uncover the rifle concealed in the backyard shed. The discovery is facilitated by a set of shed keys conveniently hidden beneath a garden statue, prompting Father Brown to question Mrs. Waterson. She makes no attempt to disguise her wartime indiscretion with Howton, albeit insisting that it is now a thing of the past, despite his threats to expose their affair to the entire village.
Father Brown then turns his attention to John, who remains steadfastly uncooperative, while Devine pays an unexpected visit to Sullivan at the station. Oblivious to her entrance, Sullivan appears to be openly flirting with another woman. Rather than confronting him, Devine leaves a note and exits discreetly. Father Brown’s interrogation of John yields no tangible leads beyond John’s open admission of his hatred for Howton and his apparent pride in orchestrating the public confrontation between Howton and Eddie.
Eddie finally steps back into his home's embrace, but his reunion with Devine is cut short by the abrupt arrival of Sullivan. A heated dispute ignites instantly as Sullivan discovers Devine's deceit about Eddie's return. Despite his efforts to justify his earlier encounter with a woman at the station as part of his job, Sullivan's explanations fall on deaf ears.
Later in the day, Mrs. Devine remains engrossed in thoughts of the altercation, while Father Brown and Brenda delve deeper into the mystery. The arrival of Goodfellow, coupled with the revelation of Howton's travel plans, prompts Father Brown to scrutinize Treadwell. Like the other suspects, Treadwell acknowledges knowing Howton but holds him accountable for his dismissal. As the list of suspects shrinks, Father Brown, assisted by Brenda, subtly prods Devine to reveal Eddie's whereabouts.
To Father Brown's astonishment, he persuades Eddie to surrender himself. During this conversation, Father Brown also notices that Eddie is missing one of his medals, which he claims to have lost while constructing a shelter. Meanwhile, Eddie places himself under Sullivan's custody, while Devine ventures into the woods armed with a metal detector, searching for the lost medal. Her search yields an unexpected discovery: Adam's bicycle, with a bullet embedded in its handlebars.
The woods soon teem with police officers, and Mrs. Waterson offers Father Brown a heartfelt recounting of the day she last saw Adam, her voice breaking with emotion. It transpires that Adam's discovery of her affair with Howton scared him into fleeing the house. Shortly thereafter, Father Brown learns that the bullet found in the bicycle matches the caliber of the one retrieved from Howton. Having confirmed the date of Adam's demise, Father Brown rushes back to the hall where the anniversary celebration was held. He spends minutes poring over the Home Guard's logbooks until he's distracted by rustling sounds outside.
In the grand expanse of the main hall, he uncovers John at the heart of a revelation that shatters illusions. Contrary to popular belief, John's romantic yearnings for Mrs. Waterson are but a misconception. Guilt gnaws at him for the fatal mishap where, amidst heightened vigilance against whispers of Nazi spies, he accidentally discharged his weapon, striking Adam, who was hampered by his deafness. Hownton, John's fellow guardsman absent at the crucial moment, later emerged to discover John's grave error and, for a decade, held this secret like a dagger at John's throat. Burdened by a crumbling marriage and dwindling finances, Hownton exploited this incident, blackmailing John until it culminated in Hownton's untimely demise.
As Father Brown unravels this intricate plot, John confesses, chaining himself to a radiator with a butterfly bomb ticking ominously, its fuse set to expire in a quarter of an hour. Devine is hastily dispatched to fetch Sullivan, whose arrival, along with Brenda, is an unexpected twist. Eddie, eavesdropping from his cell, urgently demands his release, leveraging his expertise in bomb disposal to propose mitigating the blast with sandbags.
Amidst Father Brown's soothing yet persistent efforts to calm John, Sullivan and Eddie arrive on the scene. Despite John's hostility, he reluctantly concedes to their plan, allowing them to shroud the bomb in a protective barrier of sandbags. With the clock ticking down to thirty seconds before detonation, Father Brown stands steadfast by John's side. A muted explosion ensues, yet John and Father Brown emerge unscathed from the debris, a testament to their resilience and the courage of those around them. Father Brown lauds both Eddie and Sullivan for their bravery, while Goodfellow returns Eddie's missing medal, symbolizing redemption.
Later, over scones and tea, Father Brown reveals his hand in securing Treadwell new employment. Sullivan's interruption, seeking a private word with Isabel, is met with her firm refusal. She insists that whatever he has to say, it should be heard by her friends. In an awkward revelation, Sullivan unveils the mysterious lady from his office as Gloria Hazelbrook, a local jeweler from whom he is purchasing a wedding ring. The episode concludes on a heartwarming note, with Gloria accepting his proposal and Eddie giving his blessings, a touch of hope amidst the chaos.
