Season 3 of The Marlow Murder Club premieres in March 2026 (U&Drama on March 18, 2026; MASTERPIECE Mystery! later in the year). Filming wrapped in late 2025, featuring the returning core trio: Judith Potts (Samantha Bond), Suzie Harris (Jo Martin), and Becks Starling (Cara Horgan), now officially established as civilian advisors to the newly promoted DI Tanika Malik (Natalie Dew).

The season maintains the cozy mystery charm—witty banter, eccentric British village life along the Thames, clever twists, and three standalone two-part mysteries adapted from Robert Thorogood’s novels (notably including The Queen of Poisons) and originals. High-profile victims draw media scrutiny, testing the club’s methods under public eyes.

Episodes 1–2: “The Queen of Poisons” (Adapted from the novel) The season opens with the sudden death of Marlow’s beloved mayor, Sir Andrew Waghorn—the “nicest man in town.” During a public garden party at the mayor’s residence, he collapses after sipping from a poisoned chalice (a ceremonial cup used for a toast). Initial suspicion falls on natural causes or suicide, but Judith, attending as a guest, detects the faint almond scent of cyanide and declares it murder.

The club dives in: Suzie uses her dog-walking network to uncover gossip about the mayor’s recent refusal to approve a controversial riverside development by a powerful local businessman. Becks, ever the empathetic vicar’s wife, interviews grieving family members and spots inconsistencies in the timeline. Tanika, now more openly collaborative, shares forensic details confirming poison in the cup.

Twist: The poison was meant for someone else—the mayor drank from the wrong glass in a mix-up. The real target was a rival developer who had threatened to expose corruption. The killer is revealed as the mayor’s long-suffering assistant, who had embezzled funds and feared exposure. Judith stages a re-enactment of the toast at the town hall, forcing the culprit to slip up under pressure. The episode ends with the club celebrated quietly by the community, but whispers of more high-profile cases loom.

Episodes 3–4: “Death at the Cookbook Launch” A celebrity chef, Marcus Hale (a flamboyant TV personality known for his Marlow-based restaurant), is found dead at his own cookbook launch party in a packed riverside marquee. Half the town attends—poison suspected in his signature cocktail. Police lean toward accidental overdose, but Judith notices the drink was prepared specially for him, untouched by others.

Suzie infiltrates the kitchen staff (posing as a temp helper with her dog in tow for “emotional support”), discovering a rival chef who had a public feud with Marcus over recipe theft accusations. Becks analyzes the social dynamics, realizing the victim had recently announced plans to expose industry secrets in his book. Tanika provides access to the guest list, revealing a scorned ex-partner and a jealous sous-chef.

Climax: In a tense kitchen showdown, Judith deduces the poison was applied to the rim of the victim’s glass via a tainted garnish. The killer is the sous-chef, driven by career sabotage and personal betrayal. Suzie and her dog chase the fleeing suspect across the marquee lawn in a comedic yet thrilling sequence. The case wraps with the club reflecting on how fame can poison even the closest relationships.

Episodes 5–6: “Reunion at Blackwater Manor” (Season Finale) The finale shifts to an eerie university reunion at isolated Blackwater Manor, hosted by a wealthy alumnus. A prominent guest dies mysteriously—strangled in a locked room during a blackout. Becks, an alumna herself, is unexpectedly among the attendees and becomes a suspect when her fingerprints appear on a suspicious item.

Judith and Suzie rush to the manor, working alongside Tanika amid a storm cutting off the estate. The victim was a former professor accused of misconduct years ago; the reunion was meant to clear his name but instead unearths old grudges. Suspects include former classmates with hidden motives: a betrayed student, a rival academic, and even the host.

Twist: The murder ties back to a long-buried scandal involving plagiarism and abuse. Becks is cleared when Judith proves she was framed—the real killer is the reunion organizer, who orchestrated the event to eliminate witnesses to his past crimes. In a dramatic finale, the club gathers everyone in the manor’s great hall for a classic accusation scene. Judith lays out the clues like a chess game, with Suzie using drone footage (from her growing tech skills) to expose the killer’s movements during the blackout.

Resolution: The murderer is arrested as the storm clears. Becks emerges stronger, her innocence proven, deepening her bond with the group. Tanika officially praises their “unconventional but effective” help.

Season Ending & Teaser The season closes with the trio in Judith’s riverside garden, sipping tea and scones. Judith muses, “Marlow may seem peaceful, but evil always finds a way in.” Becks shares happy news (perhaps a family milestone), Suzie introduces a new rescue dog, and Tanika drops by with wine, joking, “Next time, call me before the body drops.”

Final shot: A shadowy figure on the Thames towpath watches the house, clutching a newspaper clipping of the Murder Club. Fade to black with: “The Marlow Murder Club will return…”