As the curtains lift on another episode of "Beyond Paradise," Arthur Donalan (portrayed by Hugh Dennis) hurries indoors to dial the police, his voice tinged with urgency. He recounts a heated altercation with his intoxicated partner, who subsequently sped off in a fit of rage. Moments later, the tranquility of the night is shattered as a vehicle careens through a gateway. Arthur, hearing no response from the authorities, dials again, his anxiety mounting.
Upon awakening the next morning, Arthur is met with eerie silence; no calls have come through. Meanwhile, a woman strolling with her pooch stumbles upon a car submerged in the waters below. DI Humphrey Goodman (Kris Marshall), rummaging through his drawer, unearths an unexpected item—his Metropolitan Police handcuffs, which he forgottenly brought along. Elsewhere, Anne (Barbara Flynn) mentions her plans to donate items at the charity shop, while Martha (Sally Bretton) informs Humphrey of the removalists' impending departure and her exciting new café venture.
The police meticulously examine the grim scene and the deceased. Separate officers pay a visit to Angela Palmer (Angela Curran). DS Esther Williams (Zahra Ahmadi) heads to Ten Mile Kitchen to check in on Martha, where Zoe (Melina Sinadinou) reveals she adjusted her schedule to lend a hand with the relocation. Concerned about Zoe's workload, Esther receives a distressing call about the discovered body.
Struggling to open his stubborn desk drawer, Humphrey engages in small talk with Margo Martins (Felicity Montagu) when PC Kelby Hartford (Dylan Llewellyn) interjects with an odd query: how many sheep can fit into a Mini? Kelby explains that O'Brien's Farm has suffered a theft, with only a speed camera on the A380 capturing any footage—and it logged a Mini from the previous night. The tally of stolen sheep: eight. Skeptical, Humphrey suspects another vehicle might be involved.
Esther informs Margo about the grim discovery beneath Mousetone Bridge. Upon arrival, Humphrey learns the car is registered to 36-year-old Niall Palmer of Upper Polreath, whose disappearance was reported by his partner, Arthur Donalan, the previous night. A toxicology test is ordered by Esther.
Humphrey notices the victim sports a fitness tracker and exhibits upper body bruises. Curiously, the man wears mismatched socks emblazoned with 'Wednesday' and 'Tuesday'. Esther updates that DI Jacob Tremayne (Steve Oram) of Polmarron Station has cleared the transfer of the body. Angela Palmer, tears streaming down her face, arrives at the station, finding solace in Margo's embrace. Humphrey and Esther are introduced to Jacob and DS Fenella Foster (Gabby Best). Jacob dismisses foul play, attributing it to a vehicular accident and asserting territorial jurisdiction over the case.
However, Chief Superintendent Charlie Woods (Jade Harrison) steps in, discussing with Humphrey and Esther the command structure of the investigation. Humphrey is intent on uncovering the sequence of events leading to the accident, and Charlie concurs, greenlighting a joint operation with Polmarron's counterpart. She reveals to Humphrey that Arthur Donalan, a councilor potentially poised to become the next mayor, also sits on the Police Committee, adding an intriguing layer to the already complex narrative.
Jacob and Fenella confront Arthur, who confesses to a heated argument, culminating in Niall storming away. Arthur laments that he never should have taken the wheel, tormented by the fear that he might have caused, or suffered, a fatality. Jacob mentions Arthur's membership at St. Gerren's, prompting a brief discussion about their chief superintendent, an avid player there. Meanwhile, Esther receives a call from Fenella Foster, informing her that her inspector intends to convene a case conference at Polmarron Station. Esther suspects Jacob's motive is to assert his seniority; visiting there would grant him a strategic advantage. She instructs Humphrey to secure a neutral venue instead.
At the station, Humphrey and Esther are informed that Angela, Niall's mother, wishes to speak with the lead detective. Margo, who has known Angela for years, reveals that Niall is her son. Angela relates that Niall contacted her the previous day, desiring to return home with his laundry, as he was meticulous about his shirts being ironed by no one else and particular about his socks. She disputes the police's preliminary assessment of the incident as an accident, recalling how Niall's friend Will perished in a car crash four years prior, caused by a driver five times over the legal limit. Angela is steadfast in her conviction that Niall would never have acted similarly.
Humphrey and Esther deliberate on Angela's revelations. Humphrey assigns Kelby to retrieve a photograph of the Mini. Esther notes that Niall's fitness tracker indicated normal heart rate before spiking, and was subsequently removed at 1:06 PM, suggesting heart failure at that time. Kelby presents the photo, and Humphrey realizes Niall was behind the wheel, captured at 1:29 PM, speeding at 58 mph in a 40 mph zone. Arthur contacted authorities around 1:25 PM, prompting Humphrey to ponder how Niall could have been driving when his tracker ceased functioning six minutes earlier.
Fenella and Jacob head to Martha's café to meet Esther and Humphrey. Humphrey seeks evidence from Jacob and requests access to the vehicle report and crash investigation details. He claims indifference to Jacob's leadership, but later confides to Esther his hope that Jacob will be preoccupied with maintaining appearances, allowing them to uncover the truth about Niall Palmer. Outside, Jacob informs Fenella of his desire to monitor their movements and conversations.
Humphrey and Esther pay a visit to Arthur at his residence, warned of the urgency. As Arthur recounts the night's events, Humphrey surveys the bookshelf and inquires about Arthur's fondness for detective novels. Arthur suggests they were in the garden past midnight but struggles to recall the subject of their disagreement, which strikes Humphrey as odd. Arthur mentions that Niall occasionally stayed with him, with a recent spat escalating over moved clothing. Arthur believes Niall sped off shortly before he dialed emergency services, acknowledging Niall's aversion to drunk driving but deciding against confronting him in his inebriated state. Arthur threatens to contact Charlie Woods to understand the nature of his interrogation.
Exiting Arthur's home, Humphrey admits his mistrust of Arthur. Jacob and Fenella observe their departure, their intentions unclear.
Martha confides in Humphrey, relating her earlier conversation with Hannah about a little girl in need of foster care. She expresses concern that they rarely carve out time for themselves amidst their commitments. Martha proposes postponing the decision, but Humphrey counters by suggesting they assure Hannah of their availability while still ensuring they set aside moments for their personal life.
As Humphrey and Esther depart, Zoe and Martha are startled by a nearby crash. They rush to find Anne sprawled on the ground, clutching her shoulder in distress. Anne explains that her legs gave out beneath her, leaving her momentarily dizzy. Martha dashes off to fetch her something nourishing, just as Archie Hughes (played by Jamie Bamber) greets them warmly.
At the precinct, Margo informs everyone that Inspector Jacob Tremayne has inquired about her report. She proceeds to reveal that the lab results have arrived, sourced from Marge Atkins at Polmarron Station. The cause of death has been definitively established as drowning, with the toxicology report indicating a significantly elevated PEth level—perhaps two to three times the legal limit for driving under the influence. Esther suggests that this virtually confirms Niall's demise was an unfortunate accident.
Humphrey, however, is not fully convinced, highlighting lingering questions regarding the socks, the fitness tracker, and Niall's staunch opposition to drunk driving. Kelby informs Charlie of his intention to investigate a sheep theft before entering the station. Charlie mentions Arthur's grievance about his interview, to which Humphrey acknowledges the lack of evidence implicating Arthur in anything other than being a victim. Esther steps in to prevent Humphrey from escalating the situation further, as Charlie exits.
Jacob criticizes Humphrey's team's efforts over the phone, insisting they are only embarrassing themselves. Meanwhile, Archie kindly offers to drive Annie home, given her injury, and implores Martha to host his gathering, anticipating forty guests. Sensing Martha's hesitation, he persuades her further.
Back at the station, Esther shares with Humphrey her social media sleuthing that unveiled Paul Cresswell. After speaking with him, she learns that Paul harbors a disdain for Arthur, describing him as controlling and manipulative, with the age gap as a contributing factor. Paul believes Niall had reached his limit and was poised to confront Arthur about needing a break. Martha joins them as they watch a video of a birthday celebration Paul organized for Niall in November. She then informs Humphrey of Archie's return and the impending wine launch, agreeing to reschedule their plans. Martha extends an invitation to everyone, including Humphrey.
Margo confirms that the speed camera was recently calibrated, aligning perfectly with the timeline. Humphrey postulates that another factor might have disrupted the fitness tracker's connection, recalling the presence of a hot tub in the garden. Determined to get to the bottom of it, Humphrey seeks out Arthur for a jog and inquires about the fitness tracker. He wonders if Niall might have removed it while soaking in the hot tub. Arthur remains clueless and dismisses the matter's importance, accusing Humphrey of overcomplicating the situation.
Later, Esther warns Humphrey that he has mere minutes before he must concede that Jacob and Fenella were right all along. Kelby returns, solving the sheep mystery—a careless individual had wandered through a gate on a public footpath.
Humphrey shouts out the name "Legionella," his voice filled with urgency. The toxicology report confirms what he feared: traces of the legionella bacterium were indeed present in Niall's lungs. Humphrey explains that this type of bacterium is commonly found in stagnant water, such as that of a hot tub. Niall had a concerning 90 colony-forming units (CFU) per milliliter. Esther speculates that Niall might have inhaled some of the water from the hot tub.
Humphrey ponders how Niall was seen driving away, suspecting that he couldn't have dressed himself. He believes that Niall and Arthur had an argument in the hot tub, which escalated to Arthur drowning Niall. Margo is tasked with collecting a water sample from Arthur's hot tub to cross-check with the sample from Niall's lungs.
Humphrey suspects that Arthur dressed Niall and attempted to move the body away from the house. Arthur called the police, falsely claiming that his partner was drinking and driving. He then grabbed one of Niall's masks from a surprise birthday party, put it on, and drove past a traffic camera to mislead authorities. Arthur fled through a gate, realizing he needed to dispose of the body in water. He sent the car, with Niall's body inside, into the water and scurried back home. Upon his return, Arthur called the police again, further entangling himself in the web of deceit.
The team deliberates whether to bring in Arthur for questioning. Humphrey informs Jacob of the developments, noting that the arresting officer will have piles of paperwork to complete. Jacob's team is tasked with apprehending Arthur. Humphrey intends to inform Angela that she was right about her son's involvement.
Archie thanks Martha for hosting his gathering and expresses his belief that his mother is alright. Margo expresses gratitude to Humphrey for telling Angela the truth. Playfully, Humphrey and Archie roughhouse, resulting in Archie accidentally getting hit in the nose. He insists he's fine, brushing it off.
Kelby believes Charlie is beckoning him to join them, unaware that she is actually talking to another man. Archie strikes up a conversation with Esther, sharing tales of his travels and complimenting her on her appearance. He offers her more alcohol and guides Humphrey and Martha to a table he's set up for their date night.
Martha and Humphrey engage in lighthearted chatter, discussing their days. She teasingly asks if he brought the handcuffs, adding a spicy note to their evening. Their conversation is interrupted when Hannah calls. In a hurry, Hannah Owen informs them that the girl's mother has been rearrested, necessitating their immediate attention to care for Rosie.
