Episode 1: The Eternity Ring MI5 suspects that British atomic research has been infiltrated, and asks Foyle to investigate whether a Russian spy network could be at work in the heart of London. Episode 2: The Cage Foyle's investigation into the death of a nameless Russian leads to a mysterious military facility and the discovery that the victim was a spy with dangerous connections to British intelligence. Episode 3: Sunflower Professor Peter Van Haren gives a lecture to a group of students on the self-portraits of the artist Rembrandt, causing a young man to suffer a frightening flashback which ends in tragedy.