In the third episode of the four-part story "The Androids of Tara," the Doctor (Tom Baker) and Romana (Mary Tamm) have arrived on the planet Tara, where rests the fourth segment of the all-important Key to Time. Their mission is stymied by a power struggle between the evil Count Grendel of Gracht (Peter Jeffrey) and the soon-to-be-crowned Prince Reynart (Neville Jason). Series regular Mary Tamm not only essays the dual role of Romana and her Taran lookalike Princess Strella, but also both characters' android duplicates. Written by David Fisher, "The Androids of Tara, Episode 3" first aired on December 9, 1978.
by Hal Erickson synopsis