SAS Major Harry Maxim is assigned as a bodyguard for a nuclear strategist attending a conference.
A dying man writes a letter to a senior civil servant who commits suicide. SAS Major Harry Maxim is seconded to security at No 10. One of his tasks — to look after nuclear strategist Professor John Tyler. A Czech defector with information worth killing for — is there a connection?
The Czech defector starts a 'mole' hunt. The KGB are interested in the missing letter. Charley Farthing wants his day in court to denounce Professor Tyler, and Harry Maxim has a hard time with them all.
In France, Agnes and Maxim meet the other surviving member of the group in the photograph. In Luxembourg, Professor Tyler arrives for the European Conference — while Harbinger manipulates and Harry discovers there are no rules in their business.
