The Avengers (1961)

S6E1 The Forget-Me-Knot

Steed's associate, Sean Mortimer, arrives in a daze, aware that there's a traitor within their ranks but unable to recall much due to being drugged into an amnesiac state. As Mrs. Peel delves into the mystery, she also succumbs to the same drug, leading to both her and Sean being taken by a group of bikers. Now, it's up to rookie agent 69, Tara King, whom Steed meets through the spymaster known as 'Mother,' to step in and help turn the situation around.