Joyce is a 77-year-old retired nurse living at the Coopers Chase retirement village. She records the group's investigations in her diary, providing a warm and often humorous perspective on their daily activities. Others frequently underestimate her due to her cheerful demeanor, but she possesses sharp emotional intelligence and notices psychological details that her friends miss. She enjoys knitting friendship bracelets and selling them for charity.

Elizabeth is a 76-year-old retired MI5 spy and the unofficial leader of the Thursday Murder Club. She utilizes her espionage training, resourcefulness, and vast network of contacts to organize the group's investigations. Fearless and highly calculating, she sometimes overthinks situations by assuming everyone has hidden motives. She is fiercely protective of her husband and relies heavily on her friends' support.

Ibrahim is an 80-year-old retired psychiatrist from Egypt. He is the most cautious and cerebral member of the Thursday Murder Club, preferring to analyze situations carefully rather than rush into danger. A brutal mugging in town leaves him physically injured and severely traumatized. He retreats into his room at Coopers Chase, forcing his friends to find creative ways to reintroduce him to the outside world.

Ron is a 75-year-old former trade union leader who proudly displays his left-wing politics through a Chairman Mao tattoo. He acts as the muscle and confrontational force of the Thursday Murder Club. Divorced with an adult son, he is straightforward and spontaneous, offering a sharp contrast to Ibrahim's careful planning. He becomes deeply emotional and protective when his friends are threatened.

Donna is a Police Constable who relocated from London to the coastal town of Fairhaven. As a young Black woman in a predominantly white area, she struggles with loneliness and feels alienated from her peers. She considers the elderly members of the Thursday Murder Club her closest friends and frequently shares confidential police information with them to bypass bureaucratic obstacles.

Chris is a 51-year-old Detective Chief Inspector in the Fairhaven police force. He has recently lost weight and improved his health in an effort to impress his new girlfriend. He maintains a close, informal relationship with the Thursday Murder Club, often looking the other way when their investigations cross legal lines. He is focused on arresting a prominent local drug supplier.

Bogdan is a Polish builder who serves as a reliable associate for Elizabeth and the Thursday Murder Club. He handles various discreet or demanding physical tasks for the group without asking unnecessary questions. He is a man of few words who keeps his personal life entirely private, though he harbors a growing romantic interest in Donna.

Douglas is an active MI5 agent and one of Elizabeth's former husbands. He relies on old-fashioned charm and outdated attitudes that frequently put him at odds with modern intelligence protocols. He seeks Elizabeth's help after stealing £20 million in diamonds from a dangerous middleman and becoming the target of lethal threats.

Sue is a highly capable MI5 agent assigned to manage the fallout from Douglas's operations. She conducts interrogations with a sharp, no-nonsense approach that heavily mirrors Elizabeth's own style. She views the older woman as a worthy adversary and actively participates in the search for the missing diamonds.

Martin is a wealthy middleman who launders money and holds valuable assets as security for international criminal organizations. He lives in an immaculate house funded by corruption. When Douglas steals £20 million in mafia diamonds from his vault, Martin resorts to lethal threats to recover them before the owners target him.

Frank is a member of the New York mafia whose family owns the £20 million in diamonds stolen by Douglas. He travels to the United Kingdom to personally oversee the recovery of his property. He is violent, impatient, and fully prepared to execute anyone who stands between him and his family's assets.

Connie is a former teaching assistant who now operates as Fairhaven's primary drug supplier. She maintains a friendly, cheerful outward demeanor that masks her ruthless control over the local narcotics trade. She confidently taunts the police officers surveilling her and relies on young runners to distribute her merchandise.

Ryan is an arrogant 18-year-old who makes his living through petty theft and drug delivery. Believing he is a criminal mastermind, he shows zero remorse for brutalizing an elderly man. His actions prompt the Thursday Murder Club to orchestrate a complex scheme to ensure he faces consequences outside the traditional legal system.

Stephen is Elizabeth's third husband. He suffers from dementia, which causes him to frequently forget names, dates, and immediate events. Despite his cognitive decline, he occasionally demonstrates the brilliant intellect he possessed in his younger years. He relies heavily on Elizabeth's care and Bogdan's quiet friendship as his condition progresses.

Poppy is a newly recruited MI5 intelligence officer serving as Douglas's handler. She finds the reality of espionage distressing and openly admits she would rather be writing poetry. Her sensitive nature and visible daisy tattoo make her highly memorable to the residents of Coopers Chase.

Lance is a 42-year-old former Special Boat Service operative currently seconded to MI5. He is struggling financially following a bad breakup and spends his shifts browsing property listings he cannot afford. He was present when Douglas originally infiltrated Martin's house, tying him to the mystery of the missing diamonds.

A woman tied to the chaotic fallout of Douglas's espionage operations. She enters the orbit of the Thursday Murder Club during their investigation, presenting a complex puzzle regarding her true connections and loyalties as the retirees attempt to untangle the web of intelligence operatives.

Patrice is Donna's mother, a teacher living in London who frequently visits Fairhaven. She strikes up a romantic relationship with Chris Hudson, unaware of the immediate physical danger his police work brings to her life.

Sylvia is a widow who volunteers for the charity Living With Dementia. She carries deep grief over the loss of her husband, feeling that she lost him first to cognitive decline and then to physical death.

Kendrick is Ron's eight-year-old grandson. He is highly proficient with technology and video games like Minecraft. His straightforward, honest questions help Ibrahim slowly open up about the trauma of his assault.

Dennis is Sylvia's late husband. He suffered from severe dementia before his passing, fundamentally altering his personality and creating a prolonged grieving process for his wife.

Andrew is an armed operative employed by Martin Lomax. He is dispatched to intimidate Douglas into returning the stolen diamonds but encounters armed resistance.

Joanna is Joyce's adult daughter. She leads a busy life and rarely visits her mother at Coopers Chase, leaving Joyce to keep a pristine spare room ready for her at all times.

Gerry is Joyce's deceased husband. Despite her frequent crushes on other men, she remains deeply devoted to his memory and finds comfort in dreaming about him.

Jason is Ron's adult son. A former boxer turned minor television celebrity, his fame occasionally intersects with his father's life at Coopers Chase.

Franco is a diamond dealer based in Antwerp. He conducts international business and serves as a point of contact when the characters attempt to track the missing £20 million in jewels.