The Avengers (1961)

S06E25 Who Was That Man I Saw You with?

During a classified security mission, Tara finds herself accused of being a double-agent. In order to clear her name, she must shift the suspicion onto Steed. Meanwhile, the enemy operative Gregor Zaroff schemes to sabotage the Government's latest anti-missile defense system, known as 'Field Marshall,' by persuading Steed and Mother that Tara has leaked critical information about it.