'Just how technologically advanced are they?'
The Doctor frowned. 'Let me put it this way: they have a non-aggression pact with the Time Lords.'

The Doctor has taken his companions to paradise, or at least the clocest thing he can find. A sun enclosed by an artificial sphere where there is no want, poverty or violence.

While Chris learns to surf, meets a girl and falls in love with a biplane, Roz suspects an alien plot and Bernice considers that a Dyson Sphere needs an archaeologist like a fish needs a five-speed gear box.

Then the pease is shattered by murder. As the suspects proliferate, Bernice realises that even an artifical world has its buried secrets and Roz discovers what she's always suspected - that every paradise has its snake.

Shoreditch, London, 1963. Two teachers follow an unnervingly knowledgeable schoolgirl to her home - a blue police telephone box in the middle of a scrapyard. The old man whom the girl calls 'grandfather' is annoyed at the intrusion: there is something he has to do, and he has a premonition that he will be delayed for some time... Six regenerations later the Doctor returns; and Ace, his travelling companion, sees London as it was before the Sixties started swinging - and long before she was born. But a Grey Dalek is lurking in Foreman's Yard; Imperial Daleks are appearing in the basement of Coal Hill School; and both factions want the Hand of Omega, the Remote Stellar Manipulator that the Doctor has left behind. Has the Doctor arrived in time to deprive the Daleks of the secret of time travel?

'If you step into history,' said the Doctor, 'I won't be able to protect you.'
'This isn't history,' said Roz. 'This is family.'

The Earth Empire - the Imperium Humanum, upon which a thousand suns never set - is dying.

The Great Houses of the Empire manoeuvre and scheme for advantage; alliances are made; and knives flash in the shadows. Out among the moons of Jupiter, another battle is just beginning, as an ancient brotherhood seeks limitless power and long-overdue revenge.

The Doctor returns to the thirtieth century, searching for the source of a terrifying weapon. He fears a nightmare from his own past may be about to destroy the future. Nothing must be allowed to get in his way.

But the Doctor has reckoned without the power of history - which has its own plans for the wayward daughter of the House of Forrester.

'Oh no, not again...'

It's the ultimate in mass transit systems, a network of interstitial tunnels that bind the planets of the solar system together. Earth to Pluto in forty minutes with a supersave non-premium off-peak travelcard.

But something is living in the network, chewing its way to the very heart of the system and leaving a trail of death and mutation behind it.

Once again a reluctant Doctor is dragged into human history. Back down amongst the joyboys, freesurfers, chessfans, politicians and floozies, where friends are more dangerous than enemies and one man's human being is another's psychotic killing machine.

Once again the Doctor is all that stands between humanity and its own mistakes.

Screenwriter Ben Aaronovitch wrote Remembrance of the Daleks and Battlefield, two of the most highly regarded Doctor Who stories of recent years; his novelization of Remembrance of the Daleks was rapturously received.  He lives in north London and is, he says, not half as interesting as he would like to be.