A diamond raid in modern-day London... a secret base hidden deep in the heart of the city's sewer system... a cold and desolate planet light years from Earth... and a daring plan to alter the entire course of interplanetary history... On twentieth-century Earth it appears that the Doctor's old enemy, Lytton, has allied himself with the ruthless Cybermen. The Cybermen have devised a scheme which, if successful, could completely destroy the web of time and bring the human race to its knees. When the Cyber-planet of Mondas was destroyed in 1986 the Cybermen were forced to retreat to the planet Telos. Now they have journeyed back in time to prevent the destruction of their home world. And for Mondas to survive, the Earth must die...

The Doctor has regenerated, having sacrificed his fifth persona to save Peri's life. But things are not going well...

On this occasion the process of regeneration is by no means smooth, for the even-tempered, good-humoured fifth Doctor has given way to a rather disturbed and unsettled successor.

In a particularly irascible moment the new Doctor comes dangerously close to committing a shocking crime. Overwhelmed with guilt for his violent behaviour, the repentant Time Lord decides to become a hermit...

Tegan, the young air hostess who quite unintentionally became a member of the TARDIS's crew, wants to return to her own time, but when the Doctor tries to take her back to Heathrow Airport in the twentieth century the TARDIS lands instead on the outskirts of seventeenth century London.

The Doctor and his companions receive a decidedly unfriendly welcome - but it soon becomes clear that the sinister activities of other visitors from time and space have made the villagers extremely suspicious of outsiders.

And as a result of the aliens' evil schemes, the Doctor finds himself on the point of playing a key role in a gruesome historical event...

The TARDIS materialises on board the Vipod Mor, a galactic survey ship captained by the repulsive Orlous Moston Slarn. Things are not going too well on board the spacecraft: a mysterious killer stalks the ship's infrastructure; a junior officer, whose body is four years older than his brain, commands its bridge; the craft's computer seems to be developing its own distinctive personality; and Slarn threatens to vent his vindictive anger on his crew. Soon the Doctor and Peri stumble upon a shocking secret, a secret upon which depends the fate of the entire Universe...

THE NOVELISATION OF THE RADIO 4 DOCTOR WHO STORY.