Nat is a 47-year-old British intelligence officer who anticipates forced retirement but instead receives command of Haven, a low-priority London substation. Born Anatoly and raised in a family of anti-Bolshevik emigres, he speaks fluent Russian and possesses a practical, objective approach to espionage. He plays badminton competitively and works to balance the secretive demands of his profession with his domestic family life.

Ed is a young, passionate researcher born to a Methodist family from Northern Ireland. He holds strong political convictions, expressing vocal opposition to Brexit and right-wing nationalist movements. As Nat's regular badminton opponent, he presents a cheerful demeanor despite losing early matches, enjoying both the physical competition and post-game political debates over drinks.

Prudence is a successful pro bono lawyer working in the City of London. She originally met Nat when she handled his family's estate dispute, subsequently marrying him and moving to Moscow before deciding to raise their daughter in England. She functions as a stabilizing force in Nat's life, offering sharp legal insight and maintaining her own independent career outside the intelligence sphere.

Florence is an energetic and highly capable intelligence officer assigned as Nat's deputy at Haven. She brings a strong moral framework to her espionage work, occasionally clashing with the more detached expectations of the Service. She actively develops independent operations, including an ambitious plan to surveil a Russian oligarch, proving her dedication to her country.

Dominic is the vivacious head of London General and an old friend of Nat's from their time working together in Budapest. He oversees all Britain-based substations and promises to support Nat's field work. He is married to Baroness Rachel, a detail that connects him to high-level London real estate and finance.

Stephanie is Nat and Prudence's adult daughter. She holds anti-establishment views and has a somewhat difficult history with her father, largely due to the secrecy surrounding his long absences. She maintains an independent life and brings a grounded, civilian perspective to the family dynamic.

Codenamed Pitchfork, Sergei is a Russian student acting as a double agent for Great Britain. He comes from a lineage of Soviet intelligence officers but defected out of a stated hatred for authoritarianism. He lives a quiet life with his partner in York until receiving sudden, suspicious instructions from his Russian handlers.

Juno is a polite, well-dressed zoology graduate student studying flying bats. He plans to take Stephanie with him on a research trip to Panama and maintains a straightforward, honest relationship with her.

Arkady is a former double agent who worked for both Russian and British intelligence before accumulating significant criminal wealth. He lives in Karlovy Vary and maintains a cynical view of both Eastern and Western political systems.

Orson is a Russian oligarch living in London with ties to a Kremlin-backed crime syndicate. Florence targets his apartment for a comprehensive bugging operation due to his habit of conducting business from his home.

Madame Galina is a language tutor from the Volga region of Russia. Inherited from Nat's family, she instructs him on various dialects and scripts while checking in on his personal welfare.

Baroness Rachel is an aristocratic woman who runs a multi-million-dollar investment firm. She sits on the Treasury sub-committee that reviews intelligence operations, creating conflicts of interest in the Service.

Ilya is an intelligence agent working at the Haven substation. He serves as the duty officer who informs Nat about Sergei's urgent meeting request.

Laura is Ed Shannon's sister. She joins Ed, Nat, and Florence for a competitive game of doubles badminton at the Athleticus Club.

Bryn Jordan is the boss of the British intelligence service and head of the Russia department. He operates at the highest levels of the government apparatus, managing crises and deploying agents for special assignments.

Dimitri is Arkady's son. He drives Nat from the hotel to Arkady's guarded compound and mentions his plans to study marine biology at Stanford.