Esta serie sigue a Thomas Kell, un experimentado agente de inteligencia forzado a dejar el servicio bajo una nube de controversia. Inicialmente a la deriva y resentido, anhela la vida que perdió y el propósito que esta le brindaba. Surge una oportunidad inesperada que lo devuelve al sombrío mundo del espionaje para una última y peligrosa misión. Su búsqueda pondrá a prueba sus habilidades, desafiará sus lealtades y lo llevará a través de fronteras internacionales donde las apuestas son más altas que nunca.
Six weeks before she is due to take up her position as head of MI6, Amelia Levene vanishes without a trace. Her disappearance is the gravest crisis MI6 has faced for more than a decade. There has been no ransom demand, no word from foreign intelligence services, no hint of a defection
Thomas Kell thought he was done with spying. A former MI6 officer, he devoted his life to the Service, but it has left him with nothing but grief and a simmering anger against the Kremlin. Then Kell is offered an unexpected chance at revenge. Taking the law into his own hands, he embarks on a mission to recruit a top Russian spy who is in possession of a terrifying secret. As Kell tracks his man from Moscow to London, he finds himself in a high stakes game of cat and mouse in which it becomes increasingly difficult to know who is playing whom. As the mission reaches boiling point, the threat of a catastrophic terrorist attack looms over Britain. Kell is faced with an impossible choice. Loyalty to MI6 - or to his own conscience?