Diese Serie begleitet Thomas Kell, einen erfahrenen Geheimagenten, der unter kontroversen Umständen aus dem Dienst ausscheidet. Anfangs orientierungslos und voller Groll, sehnt er sich nach dem verlorenen Leben und dem darin enthaltenen Sinn. Eine unerwartete Gelegenheit lockt ihn für eine letzte, gefährliche Mission zurück in die Schattenwelt der Spionage. Seine Suche wird seine Fähigkeiten auf die Probe stellen, seine Loyalitäten herausfordern und ihn über internationale Grenzen führen, wo die Einsätze höher sind als je zuvor.
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?