The Doctor (Doctor Who) footage. Tom Baker did reappear, but as "the Curator", an ambiguously different character who he was not credited for playing. A voice actor, John Guilor, recorded a line of audio impersonating the First Doctor, for which he was credited as "Voice Over Artist". In other multi-Doctor stories, the multiple actors are all credited as "The Doctor", the exception being "The Three Doctors" (1972–73), which credited William Hartnell, Patrick Troughton and Jon Pertwee as "Doctor Who" as the 1972 serial preceded the practice of crediting the character as "The Doctor". In "Human Nature" (2007), the plot involves the Tenth Doctor altering
The Chase (Doctor Who) the last appearance of Russell and Hill as companions Ian and Barbara and the introduction of Peter Purves as new companion Steven Taylor. In the TARDIS, the Doctor, Ian, Barbara, and Vicki are huddling around the Time-Space Visualiser, a television-like souvenir from their recent adventure at the Space Museum, which can pick up on any past event in the whole of time and space. The TARDIS then lands, and the Doctor confirms conditions are hospitable. Ian and Vicki leave to explore the desert wilderness. They find an ancient trap door in the sand. Inside, they are trapped — and become