The Eternity Ring

S8 E1: New three-part series, set in the era of the cold war. As Foyle returns from a stay in the USA, MI5 agents persuade him to go to their London HQ immediately. Foyle is told that a Soviet spy ring called the Eternity Ring is at large in the capital and could involve the distinguished nuclear physicist Professor Michael Fraser. Foyle does not understand why he has been involved, but the deputy head of MI5 explains that Fraser's secretary is Foyle's former assistant, now married, Samantha Wainwright, whom Fraser could be using as a go-between with the Russians. Foyle is shocked that MI5 are suggesting that Sam could be a traitor to her country.