In the conclusion of the six-part story "The Wheel in Space," the Cybermen reveal their master plot to attack and take over the Earth. Back on the Space Wheel, the Doctor (Patrick Troughton) and his companions steel themselves for a final all-out assault against the Cybermen. Guest star Wendy Padbury) becomes a regular cast member in the role of Zoe Heriot. Scripted by David Whitaker from a story by Kit Parker, "The Wheel in Space, Part 6" originally aired on June 1, 1968, as the final episode of Doctor Who's fifth season. ~ Hal Erickson, Rovi