Foyle's new boss, Sir Alec Meyerson, asks him to investigate the deaths of three Russian defectors, who were all in supposedly safe houses. Then another dying Russian collapses in a hospital; his last words apparently being 'Ten Eye' and Doctor Ross, who tried to save him, is murdered after asking Foyle to meet him. In looking into the doctor's death, Foyle discovers the significance of 'Ten Eye' at a secretive military establishment which eaves-drops on Russian transmissions and decodes them for the West. At the same time, the disappearance of one of Adam's constituents seems to be linked with the defection of a woman with the same name, who was the safe houses' liaison officer. As Foyle discovers who really betrayed the Russians and killed the doctor for knowing too much, Sam helps Adam to political success.
—don @ minifie-1