The officers of the Special Branch mount a dawn raid on the homes of the members of a suspected spy ring.

A girl being held for giving official secret documents to the Russians faces a long gaol term, but an exchange offer for a Briton arrested in Moscow is offered. The officers suspect she's far more than she seems to be.

Jordan flies to Frankfurt to escort a British subject, Selby, back to England. Selby had disappeared three years earlier in East Germany and the British Government are anxious to learn what he's been up to - but the Russian KGB hide in the shadows.

Inman meets the CIA's new man in London. Jordan meets an old friend from Moscow. All perfectly legal - until the two are seen together at intervals and the Special Branch team become involved in international politics.

When Britain's top code and cypher breaker is forced to mingle with Communist players during a chess tournament, Inman goes along to keep an eye on him. Moxon, meanwhile, is playing a dangerous game of his own: the pawn being Jordan.