The Tenth Planet is the partly missing second serial of the fourth season of the British science fiction television series Doctor Who, which was first broadcast in four weekly parts from 8 to 29 October 1966. It was William Hartnell's last regular appearance as the First Doctor, and the first story to feature the process later termed "regeneration", whereby the lead character, The Doctor, undergoes a transformation into a new physical form. Patrick Troughton makes his first, uncredited appearance as the Second Doctor.
The serial is also notable as the first story to feature the Cybermen, a race of malevolent cyborgs that became a recurring adversary in later Doctor Who stories. The "tenth planet" in the title makes reference to a fictional lost planet in Earth's Solar System; at the time of production, the Solar System was generally held to consist of nine planets, prior to the redesignation of Pluto as a minor planet.
The Tenth Planet is an incomplete Doctor Who serial – one of many serials that were affected by the BBC's policy of wiping archived programmes in the 1960s and 1970s. Only three of the four episodes are currently held in the BBC archives; the last episode remains missing, although several short clips, including the regeneration sequence, have been discovered intact. In 2013, The Tenth Planet was released on DVD with a full-length animated reconstruction of its missing footage.
Plot
The TARDIS lands at the South Pole in 1986. The Doctor, Ben and Polly are taken to the Snowcap Base space tracking station. Commanded by General Cutler, the base is monitoring a crewed space probe being drawn off-course by an unknown force, and they discover a new, unknown planet approaching Earth. Recognising identical landmasses to those of Earth, the Doctor reveals it is Mondas, the Earth's long-lost twin planet.
A mysterious spaceship lands in the snow and three robotic creatures take control of Snowcap Base. They are Cybermen, former human beings who have replaced their bodies with mechanical parts, and no longer have the "weakness" of emotions. The base staff watch helplessly as the space probe is destroyed by the gravitational pull of Mondas. The Cybermen explain that Mondas is absorbing energy from Earth and will soon destroy it. They propose to take humans back to Mondas and turn them into Cybermen.
The humans mount a resistance and kill the Cybermen with their own cyberweapons. Cutler plans to destroy Mondas using a Z-bomb nuclear missile. Space Command HQ in Geneva and Cutler’s chief scientist Dr. Barclay oppose Cutler, as the radiation from the exploding planet would cause immense loss of life on Earth. The Doctor, unwell, passes out. Cutler detains the Doctor and Ben in a cabin. Ben escapes, sabotages the rocket, and the Z-bomb launch fails.
A new squadron of Cybermen arrive, kill Cutler, take control of the base, and order the Z-bomb to be disarmed. Cybermen invade Earth and take over Geneva Space Command. The Doctor realises that Mondas is absorbing too much energy and will be destroyed, and that the Cybermen plan to destroy the Earth with the international arsenal of Z-bombs to save Mondas. The Doctor and Polly are imprisoned on the Cybermen's spaceship. Ben and the base crewmembers overpower the Cybermen and regain control of the base. As more Cybermen enter the base, Mondas explodes. Disconnected from their power source on Mondas, all the invading Cybermen on Earth collapse and die, ending the invasion.
Ben frees the Doctor and Polly. The Doctor, ill, returns to the TARDIS. Ben and Polly follow, and find the Doctor has collapsed unconscious on the floor. As the sound of the TARDIS engines is heard, the Doctor is covered in a luminous light and transforms into a younger man.
Production
250px|thumb|A 2014 reproduction of a Mondasian Cyberman (on display at the [[Doctor Who Experience)]]
All four episodes of this story feature a specially designed graphics sequence used for the opening titles and closing credits. Designed by Bernard Lodge, they were intended to resemble a computer printout. In the opening credits of the first episode, Kit Pedler is incorrectly identified as "Kitt Pedler". In the opening credits of the third episode, Gerry Davis is incorrectly identified as "Gerry Davies".
William Hartnell did not appear in the third episode.
The First Doctor's final words were originally scripted as something similar to "No... no, I simply will not give in!" Time was running short towards the end of production, and director Derek Martinus opted not to record the line, wanting to ensure that the regeneration sequence was recorded as well as possible. As a result, the First Doctor's last words were simply "Ah! Yes. Thank you. That's good, keep warm." The line cut from the script by Martinus suggested that the Doctor was refusing to give in to the regeneration process. In 2017, Doctor Who writer Steven Moffat exploited this idea and created an extended narrative around the Doctor delaying his regeneration for the episode "Twice Upon a Time". The episode uses original footage from The Tenth Planet alongside new scenes with David Bradley portraying the First Doctor, encountering his future self, the Twelfth Doctor.
Cast notes
During the regeneration sequence at the end of the final episode, Patrick Troughton momentarily makes an appearance – uncredited – as the Second Doctor. This was William Hartnell's last regular appearance as the First Doctor; he would reprise the role for the tenth anniversary serial The Three Doctors.
Both voice actors for the Cybermen, Roy Skelton and Peter Hawkins, were already veterans of the series, having voiced aliens—most notably the Daleks—in several previous serials.
As a result of his role as the astronaut Williams in this serial, the Bermuda-born Earl Cameron reportedly became the first black actor ever to play an astronaut on television.
Missing episode
The last episode of this serial is missing from the BBC's archives. It is one of the most sought-after of the missing episodes, because it contains the historic first regeneration scene (even though a low-quality, truncated copy of this sequence survives and is held in the BBC Archives), and also because it is William Hartnell's final episode. As such, it is included in a list of the twenty most wanted missing programmes (as drawn up by the British National Film Theatre) alongside the BBC studio footage from the Apollo 11 landings (which is currently held only in soundtrack form).
Popular myth has it that the only surviving telerecording copy of the fourth episode was lost when loaned out to the children's programme Blue Peter in 1973 when they wished to use a clip from it in a feature on the tenth anniversary of Doctor Who.