Bernard Samson (Ian Holm) confronts the suspected mole in the Foreign Office. Meanwhile, in Berlin, Volkmann and his wife are playing a curious game of intrigue and deception.

Bernard Samson (Ian Holm) is a marked man following the exposure of his wife, Fiona, as a traitor. Meanwhile, a KGB agent in Mexico wants to defect to the west.

Samson's father-in-law threatens legal action to secure custody of the children. Bernard Samson (Ian Holm) receives a surprise visitor. Mackenzie is found dead in an MI6 safe house.

Bernard Samson (Ian Holm) goes to Mexico to try to turn Stinnes.

Bernard Samson (Ian Holm) attends a lavish Christmas party in Berlin, in the hunt for a traitor. Stinnes offers information about a KGB spy cell operating in Oxford.

Bernard Samson (Ian Holm) has to oversee one last operation to trap the KGB, and to test the sincerity of Stinnes's defection.