The Daleks' Master Plan is the mostly missing fourth serial of the third season in the British science fiction television series Doctor Who, which originally aired in twelve weekly parts from 13 November 1965 to 29 January 1966. This twelve part serial is the longest with a single director and production code. (The Trial of a Time Lord was longer but was made in three production blocks, with separate codes, and with four separate story lines each with their own authors and working titles)
This serial marks the final appearance of Adrienne Hill as companion Katarina, the only appearance of Jean Marsh as Sara Kingdom. Katarina and Sara Kingdom both died during the serial, marking the first two companion deaths in the show. Episode 1, "The Nightmare Begins", marks the first appearance of Nicholas Courtney in Doctor Who, here playing space security agent Bret Vyon.
It was the second Doctor Who story never to be screened in Australia, as the Australian Broadcasting Corporation judged the story to be unsuitable for children. Only three of the twelve episodes (two, five and ten) are held in the BBC archives; nine remain missing.
Some six months after the events of "Mission to the Unknown", the TARDIS arrives on the planet Kembel, and the First Doctor leaves the TARDIS to try to find medical aid for the wounded Steven, leaving him with the Trojan servant girl Katarina. Meanwhile, a Space Agent, Bret Vyon is also on the planet trying to find out what happened to Agent Marc Cory. After a less-than-amicable meeting with the TARDIS travellers in which he holds them at gunpoint and demands to be taken away from the planet, Vyon helps cure Steven and agrees to work with them to escape and warn Earth of the massive Dalek-led alliance that is amassing on the planet. Part of this alliance is the treacherous Guardian of The Solar System, Mavic Chen, who has brought a sample of the extremely rare Taranium, which will become a key part of the Daleks' ultimate weapon, the Time Destructor. The Daleks soon learn of their presence on the planet and the Dalek Supreme gives the command for Operation Inferno to be carried out, burning down the jungle. The travelers shelter at the Dalek city. The Doctor manages to steal the Taranium by impersonating delegate Zephon, and he, his companions and Bret escape on Chen's ship, termed a Spar.
The Daleks exterminate Zephon for allowing the Doctor to impersonate him and they then cause the Spar to crash on Desperus, a penal planet where prisoners are left to fend for themselves. Mavic Chen departs for Earth in a temporary ship, wanting to find out exactly who the people who stole the Taranium are. On Desperus, the Doctor repairs the ship, and they escape when the pursuing Dalek ship itself crashes upon arrival. However, a convict named Kirksen sneaks aboard the Spar prior to take-off and holds Katarina hostage in the airlock once the ship has left Desperus. He demands to be taken to Kembel or else he will kill Katarina, but she sacrifices herself by opening the airlock, forcing them out into space. The Daleks warn Chen that the fugitives will be heading for Earth to inform them of their presence on Kembel, and order him to kill them on sight and snatch the Taranium core. Chen worries that that would make the Space Security Service realise he is a traitor, so he instead tells everyone on Earth that the Taranium core is actually a vital substance needed to keep the peace. Space Security Agents patrol all corridors and guard all offices, and all landing bays are monitored for the arrival of Chen's Spar.
After mourning Katarina's loss, the party arrives on Earth and meets a contact of Vyon's, who is in league with Chen. Bret kills him but seconds later another Space Agent, Sara Kingdom arrives and kills Vyon (who it later transpires is actually her brother) and attempts to get the Taranium from the Doctor and Steven, but they escape. She pursues them to a laboratory, where they are caught in the middle of a molecular dissemination experiment and are inadvertently transported to Mira, a planet populated by savage invisible creatures, where the three enter into an uneasy alliance. They are constantly attacked by the creatures, the Visians, and try to take shelter.
On Earth, Mavic Chen is distraught, believing that the Taranium was destroyed during transportation. However, the scientists carrying out the Dissemination inform him that the computers are registering that the matter that has been transported (a cage of mice) has successfully arrived on Mira. Chen angrily says that this is no evidence that the taranium wasn't broken up into pieces. He believes he will be exterminated by the Daleks for his failure, so when he makes his report to them, he says he lured the fugitives into the laboratory, as their presence on Earth would have caused suspicions of the Dalek plan, and tells them to pick up the Taranium from Mira whilst he returns to Kembel. When the Daleks arrive they are attacked by the invisible creatures, and the Doctor, Steven and Sara commandeer the Dalek ship and escape. It turns out that the Daleks can pilot the ship remotely and bring it back to Kembel, but the Doctor is able to create a fake Taranium core, which they hand over to the Daleks before escaping Kembel in the TARDIS.
After a brief interlude in which the Doctor and his companions journey to a police station in 1960s England and then a silent film set in America, the trio toast Christmas, and the Doctor breaks the fourth wall by wishing a happy Christmas to the viewers at home.
On Kembel, the Daleks test the Time Destructor on delegate Trantis. It has no effect, and the Daleks realise it is a fake. A taskforce of Daleks disembarks to chase the travellers, intending on recapturing the real core. Meanwhile, The TARDIS arrives on a volcanic planet where the Doctor has a run-in with his old enemy, the Meddling Monk, who attempts to sabotage the TARDIS in revenge for the Doctor previously stranding him in 11th century England. The Doctor is still able to fly the TARDIS to Ancient Egypt, though he has to stop there for repairs. The Monk follows him, as does the Daleks and Mavic Chen. The Monk, Sara and Steven are captured and used as hostages, and without time to create another fake, the Doctor is forced to hand over the real Taranium core. They escape when some Ancient Egyptians attack the Daleks which they describe as 'war machines'. Knowing that the Daleks will now carry out their invasion, the Doctor steals the directional control from the Monk's TARDIS, so that they can return to Kembel and stop the Daleks. The Monk unwittingly ends up on a desolate, icy planet, and realises he can no longer control the destination of his TARDIS.
The Doctor returns the TARDIS to Kembel, where Steven and Sara (who get briefly separated from the Doctor) discover that the Daleks have turned on their allies, including Chen, and imprisoned them before apparently leaving the planet. The two TARDIS travellers free the alien leaders, and they leave to persuade their governments to ally against the Daleks, though Chen appears to die when his Spar explodes during take-off. Steven and Sara then find an underground base being used by the Daleks, only to be captured and held at gunpoint by a delusional Chen, who marches them into the base and the Dalek control room. He tries to proclaim himself the leader of the Daleks, but they dismissively kill him.
Now reunited with his companions, the Doctor activates the fully assembled Time Destructor. Knowing that the device will quickly begin ageing anything in its vicinity, the Daleks allow the Doctor to escape with Steven and Sara. Steven goes ahead back to the TARDIS, but Sara insists on accompanying the Doctor. The two are unable to get back to the TARDIS before the Time Destructor reaches full power, and Sara is aged to death and reduced to dust metres away from the TARDIS. Steven helps the Doctor back inside and, freed from the Destructor's influence, the two are left weakened, but alive and back to their original ages. The Daleks try to destroy the Time Destructor, but instead cause it to run out of control, resulting in it destroying the Daleks and all life on the planet. The Doctor and Steven emerge from the TARDIS, and Steven is distraught over the deaths of Bret, Katarina and Sara, while the Doctor can only contemplate the "terrible waste" that has taken place.