This story was twelve episodes long, the longest single Doctor Who story, but only three episodes exist. The TARDIS arrives on the planet Kembel and The Doctor leaves to find medical aid for the wounded Steven, leaving him in the care of the Trojan servant girl Katarina. Meanwhile, a Space Agent named Bret Vyon (Nicholas Courtney) is trying to find out what happened to agent Marc Cory, who was killed by the Daleks in Mission to the Unknown. He cures Steven and the time-travellers agree to work together to stop the Dalek Alliance. They escape in Vyon’s ship before the Daleks can burn down the entire jungle.
The ship crashes on Desperus, a penal colony planet, and they are once again under attack. Katarina sacrifices herself to save them, ironic considering that she thought she was being taken to the afterlife. This was the first death of a Doctor’s companion. The rest travel to Earth, where they are betrayed by another Space Agent named Sara Kingdom, played by Jean Marsh of Upstairs, Downstairs fame. They are caught in a molecular dissemination experiment which transports them to Mira, a planet of savage invisible creatures. When the Daleks arrive in pursuit, they are attacked by the invisible creatures and The Doctor, Steven, and Sara escape in a Dalek ship. They journey to a Police Station in 1960’s England and an American silent-film set, raise a toast to Christmas, and wish a happy holiday to Doctor Who fans at home. Seriously. A scary and violent Dalek story was thought to be inappropriate for Christmas.
The Daleks force The Doctor to work on their new weapon—the Time Destructor—but it fails, and they realize The Doctor has sabotaged the mechanism, after he has escaped. The TARDIS arrives on a volcanic planet where the Doctor runs into the Time-meddling Monk, who tries to sabotage the TARDIS in revenge for being stranded in 11th Century England. The Doctor gets away but is forced to stop in ancient Egypt for repairs. The Monk follows him, as do the Daleks. The Doctor is forced to help the Daleks fix the Time Destructor. The Doctor steals the Monk’s directional circuit and the Monk ends up stranded again on a desolate icy planet.
The Doctor is able to go to Kembel where Steven and Sara discover that the Daleks have turned against their allies. They free the aliens and they leave to warn their home planets of the Daleks’ treachery. The TARDIS crew barely escape, weakened, except Sara Kingdom, who is caught in the Time Destructor field and aged to death. The Doctor has sabotaged the weapon and the Daleks lose control and it kills them along with all life on the planet.