The Doctor is captured by the Cybermen and taken back to their home planet. There he discovers the source of the signal. Cyrons, original inhabitants of the Cybermen's world survive and they want the Cybermen gone. The Doctor learns the full extent of the Cybermen's plans. Not only are the Cyrons threatened but so too the very future of the human race. This is no war of conquest, but total destruction.
The TARDIS makes an emergency landing on Varos, a planet that used to be a penal colony, and where the native Varosians are presently entertained by broadcasts of real violence and death. Mistaken for rebels, the Doctor and Peri learn that Sil, an evil delegate of the Galatron mining corporation, bids to rule Varos and to control supplies of Zeiton 7 ore, which is the TARDIS's only fuel source.
In a 19th century mining village, a renegade Time Lady known as The Rani is draining brain fluid from local men, turning them savage and berserk. It is here The Master plans to coerce her help in his vengeance upon The Doctor while also establishing a power base for controlling Earth's future.
The Master uses The Rani's mind-controlling parasites to keep a meeting of Earth's leading scientists from being canceled, and helps The Rani plant transformation land mines for The Doctor as he continues to propose an alliance with her in ruling over Earth.
The Time Lords have dispatched the Doctor (in his 2nd incarnation) along with Jamie to a space research station to see Dastari, the Director of Projects, about dissuading two of his scientists from further experimentations on time travel that are rattling the fabric of time. The Doctor is further alarmed over Dastari's latest genetic experiments, boosting the intelligence of a bestial and carnivorous humanoid race called the Androgum. This secondary concern soon proves the greater problem: the Androgum have sided with the Sontarans to take over the station. The ...
With carnage and decay all about the space station, Doctor No. 6 and Peri continue to avoid the automated defense system trying to kill them, but there's also something alive lurking about with an eye on them as well. Evidence suggests the Time Lords are responsible for all this, but the Doctor refuses to believe it. He may be wrong, and he also fears a pinhole has been poked into the bubble that is the universe, with total and unstoppable annihilation to follow. Far away, Doctor No. 2 is about to be dissected by the Sontarans and the Androgum in order to find the ...
Closing in on the goal of time travel, the Androgum and Sontarans get set to double-cross each other. With Peri and Jamie alternately in danger of winding up on the bill of fare, the decision is made to genetically transform Doctor No. 2 into an insatiably carnivorous Androgum, which causes Doctor No. 6 to develop a sudden taste for house cats as he races to not let this change become permanent.
A time corridor, called Timelash, has been set up to punish dissidents on the planet Karfel, dumping them alive but permanently into Earth's early history. The TARDIS runs right into it, and the Doctor thereafter finds a society with advanced technology it shouldn't have along with an unnerving absence of reflective surfaces of any kind.
For his impending confrontation with the mysterious and cloistered Borad, dictator of Karfel, the Doctor takes kontrom crystals from the Timelash to build a 10-second time break device, not knowing of the Borad's mutation and breeding plans for Peri or the interplanetary war he's sparked with the Bandrils, who are on their way to destroy all mammalian life on Karfel.
The Doctor and Peri arrive on the planet Necros to attend the funeral of scientist Professor Athur Stengos, only to discover Davros, the creator of the Daleks, has become "The Great Healer" who runs Tranquil Repose, a facility where the terminally ill are kept in suspended animation until a cure is found. They learn Davros has been turning all those in suspended animation into Daleks that are loyal to himself while making food from their dead bodies.
The Davros running Tranquil Repose has only been a figurehead - literally just a head, created and animated by Davros himself. Now, the real Davros wheels forth to face the Doctor, but his own immoral dealings have fostered an uneasy surrounding situation, riddled with treachery, that only a few might escape.