Following a collision between the TARDIS and another time machine, the crews of both vessels find themselves trapped in a mysterious city where time doesn't flow normally, ruled by a monstrous leechlike being called the Process. A subplot follows events developing back on the origin planet of the other time travelers — the Doctor's home planet Gallifrey in a long-ago time before the Gallifreyans made themselves Lords of Time.
This novel contains examples of:
- Eldritch Location: The city, a rundown ruin divided into three by rivers of mercury where three separate timestreams (past, present and future) all exist simultaneously adjacent to each other, is actually the remains of the TARDIS following the accident, converted into its new form by the Banshee Circuit to prevent its destruction. The mercury rivers are actually the ship's fluid links, and the Doctor can control and reshape parts of the city by tapping into the TARDIS' surviving circuits.
- Have We Met Yet?: Because of the way time is distorted in the city, the first time (for her) that Ace meets the Phazels, they already know who she is. From her point of view, she meets their earlier selves a little later.
- A Head at Each End: The Process, being a giant leech.
- Living Battery: The prototype Gallifreyan time capsule is powered by the psychic energies of its crew. "Battery" is an official title of one of the crew members.
- Mad Oracle: Subverted. The Pythias were the seers who ruled Gallifrey before Rassilon came to power. The last Pythia goes mad because she's losing her oracular abilities, and can no longer see the future clearly.
- Magical Eye: The Pythia steals an eye from a decapitated Sphinx and substitutes it for one of her own, to boost her waning prophetic powers.
- Mind Screw: It's a very strange book. The various Timey-Wimey Ball shenanigans and the bizarre nature of the Eldritch Location, hinting at the near-infinite powers of the TARDIS, can be quite hard to get your head around.
- Mother Nature, Father Science: Early Gallifrey is at a crossroads, with two groups struggling to control its development: a group of male scientists (led by Rassilon) and a group of female witch-priestesses (led by the Pythia). At the end of the novel, Rassilon scores a decisive victory over the Pythia, opening the way to the foundation of the Time Lord society of the Doctor's time.
- Taking You with Me: The Pythia attempts to take all of Gallifrey with her.
- Timey-Wimey Ball: The main setting is a literal Timey-Wimey Ball — the inside of a sphere, about three miles across, containing the same city at three different points in time. At the start, things that change in the 'past' city affect the 'present' and 'future' ones, but as the book progresses, those rules begin to break down and the place ends up as a Timey-Wimey Ball in every sense.