D16 Agent Irwin Gunner was on the trail of a double agents known as White Rat in 1960 when an arranged trapeze accident caused him to suffer amnesia. 17 years later he begins to regain his memory and vows to track down the Rat, who has certainly moved up in the world by now. As Steed, Purdey and Gambit race to catch up with the long lost agent known only to them as 'Flyer', the White Rat ans his accomplices do the same in order to silence him.
—The TV Archaeologist