In the 22nd century, all the planets in the solar system are linked by a train line linked through hyperspace, so you can hop on a train in London and be on Pluto forty minutes later. And they're just about to open the first interstellar extension, connecting to Arcturus. But when the new link is opened, something goes horribly wrong...
The Doctor investigates, with the assistance of a university student named Kadiatu Lethbridge-Stewart, the great-great-great-great-granddaughter of his old friend Brigadier Alistair Lethbridge-Stewart.
This novel contains examples of:
- Black Belt in Origami: The Doctor gets past some Japanese mooks by using the court dialect of the Japanese royal family. They recognised it, but didn't understand it, which was just as well, since he said "Make way, for I am the official keeper of the Emperor's penguins and his majesty's laundry basket is on fire."
- Dog Food Diet: The Future Slang glossary at the back includes "Petfood Monster" for an extremely poor person.
- Genius Loci: It's revealed that the Sol Transit System has become so complex that it has evolved sentience.
- Instant A.I.: Just Add Water!: Transit has a weird (possibly parodic) variant of the "any system will become self-aware if it's just complex enough" version — where the system in question is the much-extended future equivalent to The London Underground.
- I Regret Nothing: Played with. The Doctor and Kadiatu are caught in a crashing plane on Mars. Kadiatu hears him humming.Kadiatu: What's that noise?
The Doctor: Edith Piaf. Born on a doorstop and sang the blues.
Kadiatu: I'd sing the blues, if I'd been born on a doorstep. What's the song about?
The Doctor: Regret.
Kadiatu: What did she regret?
The Doctor: Absolutely nothing.
[they hit the ground]
- Mythology Gag: Several are packed into the scene where the Doctor is looking through Kadiatu's library and finds a recording of an opera inspired by one of his earlier adventures. The adventure in question recognisably "Battlefield", also written by Ben Aaronovitch. The opera is said to be by "Marconi Paletti", a Tuckerization of Marc Platt, who wrote the novelisation of "Battlefield". And the title of the opera is Il Dottore Va in Viaggio, meaning something like "The Doctor Goes on a Journey", which could be rendered as Doctor On The Go, making it an extension of the gag in "Remembrance of the Daleks" (also by Aaronovitch) where the Doctor is seen reading Doctor In The House — or as The Doctor in Transit, giving us the Doctor in Transit watching The Doctor in Transit.
- Portal Network: The Sol Transit System of portal-trains just covers the solar system (although the book describes an attempt at a Stellar Tunnel). Most people have a better idea of the shape of the network than of the physical system. It's a parody of The London Underground and the Channel Tunnel.
- Tele-Frag: There are occasional references to the Bad Accident, which is eventually explained as what happened when two STS trains tried to materialise in almost the same place at the same time. They ended up merged together. And so did everyone on board.
- A True Story in My Universe: There's an opera based on the events of "Battlefield".