A story never broadcast on North American television....The Tenth Planet.  The final story for the First Doctor,
and the first to introduce the villainous Cybermen.  This video presents restored film prints of the existing first three
episodes.  The missing final, fourth episode is "reconstructed" using the few surviving film clips (including the regeneration
scene), telesnap photographic stills taken of the episode as it was broadcast, and a complete restored soundtrack
recording of the episode from when it was broadcast.
 

Serial: DD  Episode Nos. 131, 132, 133, and 134 (reconstructed.  Title: The Tenth Planet

The TARDIS arrives at a South Pole space tracking station in December 1986, just before the entire world is visited by
an entire other world... a long missing tenth planet called Mondas.  Its gravity draws a routine space shot off course,
it begins draining the Earth of its energy, and its inhabitants attack the base and the globe.  These inhabitants are called
Cybermen, who have managed to survive on Mondas by almost completely replacing their bodies with mechanical and
cybernetic parts, and now plan to do the same to the people of the Earth....

This story sees the departure of William Hartnell as the Doctor, and of course the Doctor's first regeneration.
It is also the debut story for the Cybermen.

starring William Hartnell as Dr. Who, Michael Craze as Ben, and Anneke Wills as Polly.  Written by Kit Pedler and Gerry Davis, Produced by Innes Lloyd, and Directed by Derek Martinus.

Originally transmitted from 8 Octobet 1966 to 29 October 1966 on BBC1.