Wolfsbane (1978)

Thomas' third novel is a bit of a departure from the pattern he has established. It's a bit of a period piece. The first chapter takes place in 1944 in Nazi-occupied France. British agent Richard Gardner is betrayed and captured. He escapes and vows to agent himself on the man who betrayed him.

The rest of the book takes place in 1963. Events have conspired to return Gardner to France for a holiday. There he sees a face from his past which sets him off on his hunt for vengeance.

Gardener can't know it but he has been manipulated by forces eager to expose a Soviet agent code-named "Wolf".

The novel features a young Aubrey and Latymer (from Rat Trap). The experiment of an early Cold War period piece had never been repeated which is a pity, although we do get half a WW2 novel with Emerald Decision.