Foyle's new boss at MI5 is Sir Alec Meyerson, who has replaced the traitor Sir William Chambers from the previous episode. Recognizing that Foyle can help shake up the complacent spy agency, Sir Alec asks him to investigate the deaths of three Soviet defectors, who were betrayed from their safe houses. Clearly, another mole is on the loose!
Could it be a Foreign Office translator named Evelyn Greene? She knew the addresses of the safe houses and has disappeared, apparently to East Berlin. Coincidentally, Adam encounters the same name during canvassing for a seat in Parliament, when a woman in a bombed-out building tells him that her daughter, Evelyn Greene, has gone missing.
Before Foyle can get far in his investigation, another Russian turns up badly injured at a London hospital and promptly dies, uttering a phrase that sounds like, “ten-eye.” Later the physician who treated the Russian, Dr. Ian Ross, is murdered. Foyle discovers the doctor’s body after arriving for a planned meeting. He learns that the night before, Ross had responded to an automobile accident near Barton Hall, a top-secret military installation.
A visit to Barton Hall turns up two clues. First, “Tin Eye” is Lieutenant Colonel Galt, the commander of the station, who wears a monocle. Second, although the function of the facility is a mystery, Evelyn Greene may be present, since Sam finds a bow to a woman’s shoe that matches the pair Evelyn was wearing the day she disappeared.
When Foyle questions Barton Hall’s second in command, Major James McDonald, he reveals he was in a car accident nearby and admits to detaining the Russian, but he disavows any responsibility for the man’s death. Digging deeper, Foyle recruits Danny Willis, a former Special Operations agent, to infiltrate Barton Hall. Danny succeeds spectacularly, discovering Evelyn’s cell, freeing her, and establishing that the facility is a psychological interrogation unit that uses torture to extract information from enemy agents.
Since Evelyn is not the same Evelyn Greene from the Foreign Office that presumably betrayed the defectors, Foyle is missing a crucial piece of the puzzle: Why was this Evelyn detained? The breakthrough comes in routine police work, which establishes that Major McDonald and the Foreign-Office Evelyn were left-wing lovers from their university days. Further, Foyle has noticed that McDonald has an infected tick bite; tick diseases were Dr. Ross’s speciality.
When confronted, McDonald, who is dying from tick-borne encephalitis contracted when he took Evelyn to East Berlin, confesses that the Russian escaped from Barton Hall after revealing that Evelyn was his contact. McDonald had tried to kill the agent but didn’t finish the job. He traced the bleeding man to the hospital. Assuming that Dr. Ross had recognized him in his hiding place, McDonald later killed the doctor, unaware that Ross had discovered at the previous night’s car accident that McDonald was infected with encephalitis and wanted to warn him.
Since, Lieutenant Colonel Galt heard the Russian agent implicate Evelyn Greene, McDonald had to round up someone with that name. He settled on the young woman from the bombed-out building.
Meanwhile, parliamentary voting day has arrived and Adam is elected—despite campaign shenanigans by his opponent and by his own supporters.