The episode kicks off with Brenda Palmer (Ruby-May Martinwood) receiving an enigmatic invitation from Dr. McClurgy (Sylvester McCoy), beckoning her back to the quaint Hazelnut Cottage. As Father Brown (Mark Williams) and Mrs. Devine (Claudie Blakley) present the letter to her, Brenda reminisces about their unforgettable times there, until one mysterious day when Dr. McClurgy inexplicably sent her away to a children's home. Holding the letter tightly, Father Brown hints that this could be her final opportunity to uncover the truth.
Upon arriving at Hazelnut Cottage, Dr. McClurgy not only denies authoring the letter but also appears oblivious to Brenda's presence. Father Brown harbors suspicions that the doctor might not be the true author. Conversely, Dotty Finglesham (Melaine Walters) warmly envelops Brenda in an embrace and invites her over for tea, eager to share her insights about McClurgy. Dotty confesses to penning the letter, hoping a reunion with Brenda would rejuvenate McClurgy's spirits. She describes Butterley Rise as a delightful place, yet admits it can sometimes be eerily serene. She further divulges that Lord Sprocket (Owen Brenman) has commissioned a property developer, Edward Wainsbody (Nick Blakeley), to construct new bungalows for the residents.
Moments later, Lord Sprocket and Edward are publicly humiliated by Dr. McClurgy, who firmly declines another offer for his property. Incensed, Edward retaliates by announcing a town meeting at Butterley Meadow for 2 o'clock.
As Brenda strolls through the meadow with Father Brown and Devine, she spots a familiar face in Susan Payne (Jasmine Bayes). Upon introduction, Susan reveals herself as a fellow evacuee and an illustrator for the British Nature Review. Dotty then reappears, accompanied by several locals. Tensions escalate when Edward unveils his plan to relocate the project to the meadows. Susan emerges as the most vehement critic in the crowd, culminating in her hurling a glass of water in Edward's face. After Sprocket and Edward hastily retreat, Dotty blames McClurgy's obstinacy for the impending loss of the meadow. Father Brown encourages Brenda to pay McClurgy another visit, perhaps seeking clarification amidst the swirling chaos.
McClurgy is lost in nostalgic reverie, leafing through faded photographs of his beloved, late wife, when Brenda unexpectedly reappears at his doorstep, her voice imbued with a plea for him to recall her presence with fondness. Upon withdrawing indoors and reappearing moments later with a magnifying glass in hand, McClurgy's recognition of her is instantaneous. Inside, Brenda's gaze swiftly scans the cluttered, mold-infested environment, realizing that this dilapidated state of his home is what ails him. Just as their reunion begins to blossom, a brick, seemingly summoned from thin air, shatters the front window, abruptly halting their tender moment.
In the meadow, Brenda swiftly identifies Edward and Sprocket as the likely culprits of the vandalism, her accusations falling heavily upon them. Sprocket, innocent of the charge, vehemently denies any involvement, while Edward responds with a callous chuckle. Brenda, still seething with anger, vents her frustrations to Devine, who seizes the moment to inquire about McClurgy's reasoning behind sending her to the children's home. Brenda confesses her inability to broach the sensitive subject. Father Brown's timely arrival into their conversation paves the way for Devine's proposal—a picnic with McClurgy the following morning, to which Father Brown gracefully agrees.
Returning to the meadow, Brenda, Devine, and Father Brown encounter Sprocket in a desperate search for his missing dog, Chumleigh. As a united group, they soon uncover an ominous discovery: Edward's buried body, which has inadvertently captured the dog's attention. Sergeant Goodfellow (played by John Burton) and Inspector Sullivan (portrayed by Tom Chambers) step into the investigation, grilling Father Brown, yet it is the clergyman who emerges as the beacon of clarity. He uncovers inconsistencies, noting that the grave was intended for someone much taller and finding a gold rat charm belonging to the "Grand Order Of Water Rats," a benevolent society comprising showbiz performers. Father Brown expresses skepticism regarding Edward's membership in such an esteemed circle.Although Dotty isn't overly devastated by Edward's passing, she is taken aback by McClurgy's grim outlook on life. Soon, the conversation steers towards the omnipresent mold, prompting Brenda to reminisce about the cottage's former pristine state. McClurgy attributes his meticulousness to a "very significant" houseguest he once hosted, a revelation that prompts Brenda to inquire about the reason behind her dismissal. He responds by saying that he was growing old and saw no end to the war. Dissatisfied with his answer, Brenda storms off to the garden, where Father Brown notices muddy footprints trailing towards the street—an ominous sign.
Moments later, a police car glides by with Susan in the backseat. Upon visiting the police station, it transpires that authorities have traced a wool fiber from the corpse to Susan's sweater. She confesses to an attempted apology that escalated into a physical altercation, explaining the discovery. After further interrogation, Father Brown heads back to Dotty's cabin to inquire about her presence in the meadow.
Dotty clarifies that she was visiting a memorial she had erected for her deceased husband. Though his body was never retrieved after his plane was shot down, she has planted countless wildflowers in his honor. Alongside Brenda and Devine, Father Brown ventures back to the meadow to confront Sprocket about an alleged argument that Dotty overheard.
However, Sprocket is nowhere to be seen. Father Brown searches the tent pitched in the meadow, which turns out to be the hub of a development project. He uncovers blueprints and a land contract almost immediately. Sprocket interrupts just as Father Brown makes these discoveries. Incensed by the intrusion, Sprocket eventually admits that Edward had gotten him drunk and duped him into signing away a hectare of land. The meeting concludes with Sprocket revealing that he has already hired a new developer.
Devine's dreams of a quaint picnic quickly evaporated when Father Brown began inquiring about the muddy footprints with McClurgy. McClurgy insisted that the prints terminated at the street gate, marking the point where his anxiety had overwhelmed him, forcing him to halt. McClurgy's seclusion, exacerbated by whispers of a German airman residing within the mysterious Butterley Woods, had transformed him into a recluse and prompted him to send Brenda away.
Armed with new information, Father Brown ventured back to the police station to interrogate Susan, who claimed to have glimpsed the airman during one of her woodland escapades. Susan corroborated her story, disclosing that she had seen him again three weeks later, imprisoned in a dimly lit woodshed. She also observed a foot injury, presumably sustained from his daring leap from the aircraft.
Upon returning to McClurgy's cabin with Susan's tale, Father Brown found Brenda and Devine had shifted their picnic indoors. Sharing Susan's account and delving deeper into the conversation unveiled that Dr. McClurgy himself had treated the German's wounds. Similar to Susan, McClurgy professed ignorance regarding the shed's owner. Without a word, Father Brown abruptly rose and exited.
Moments later, he was revealed sitting in Dotty's shed, awaiting her return. It transpired that she had killed the German in self-defense. After Susan had released him, he had broken into Dotty's home, desperate to find means for his return to Germany. The body would have remained undiscovered in the meadow, concealed by nature's embrace, had it not been for the encroaching development project.
Father Brown eventually persuaded Dotty to surrender herself to the authorities, while Brenda miraculously convinced McClurgy to proceed with Sprocket's ambitious restoration venture. Even more astonishingly, she coaxed him to deliver the news in person, stepping bravely into the open air.
