Its surface ravaged by colliding time-fields, the planet Hirath is a patchwork of habitable areas separated by impenetrable zones of wild temporal fluctuations.

The planet's unique biosphere is being exploited by an uncaring company happy to rent out temporarily isolated chunks of the planet to the highest bidder - no questions asked.  But the controlling computer seems to be malfunctioning, and the viability of the whole planet hangs in the balance - along with countless thousands of lives.

Arriving at Hirath's control base, the Doctor and Sam are soon separated and trapped on the dying planet.  While Sam becomes the focus of attention in a barren penal settlement, the Doctor discovers the secret of Hirath's unique condition - just as a race of hideous bloodthirsty alien creatures arrive in force to reclaim it.

Caught up in a desperate struggle for survival, it seems time has run out for every living creature on Hirath - not least Sam and the Doctor...

The TARDIS has finally brought the Doctor and Sam back to Earth - and straight into danger.

It is 1963.  Six very different people have been gathered together for study by parapsychologist Charles Roley in his stately home outside London.  All of them claim to have been possessed by the devil, and have shared similar delusions - they describe the same bizarre 'death cave' riddled with demons.

Roley's experiments are having a gradual yet terrifying effect on his subjects, and the Doctor and Sam discover the connections between those tainted with the madness are more disturbing than anyone could guess.

For the Doctor, too, has seen the cave they describe - on a dead world, billions of years ago.