Blake's 7 (1978)

S4E3 Traitor

The planet Helotrix, like numerous other star systems, is succumbing to the effects of a newly developed Federation pacification drug. Tarrant and Dayna beam down to the surface to conduct their investigation. Meanwhile, Servalan, having lost her position as Federation president, has returned incognito as Commissioner Sleer, erasing all traces of her former identity.