The Algebra of Ice (novel)

 was the sixty-eighth BBC Past Doctor Adventures novel. It featured the Seventh Doctor, Ace and Alistair Gordon Lethbridge-Stewart. This is the first Past Doctor Adventures novel to feature this line up of Doctor, companion and Lethbridge-Stewart.

Publisher's summary
A genius maths nerd, a weird webzine publisher, and the Doctor's old ally, the Brigadier, find themselves helping the Doctor and Ace solve what should be a simple puzzle: the appearance of a crop circle in the Kentish countryside.

Hardly uncommon. But there are some peculiar features. It's not a circle but a series of square-sided shapes. It's filled with ice. And it draws the Doctor and Ace into a confrontation with a reality right next to zero.

Plot
to be added

Characters

 * Seventh Doctor
 * Ace
 * Brigadier Lethbridge-Stewart
 * Ethan Amberglass
 * Adrian Molecross
 * Clisby
 * Patrick Unwin
 * Sheridan Brett
 * Sergeant Ramsey
 * Jessica Tilbrook

Continuity

 * The Doctor recalls destroying Skaro, (TV: Remembrance of the Daleks) but also mentions he hasn't destroyed his own homeworld. (PROSE: The Ancestor Cell, TV: The End of Time)
 * Visiting Ethan Amberglass whilst in hospital, the Doctor mentions that he has just visited both his own mind and the Moon. (PROSE: Timewyrm: Revelation)
 * Earlier in his personal timeline, the Seventh Doctor visited Pompeii on 23 August 79 AD in the company of Melanie Bush (AUDIO: The Fires of Vulcan) and would later do so again in his tenth incarnation in the company of Donna Noble. (TV: The Fires of Pompeii)
 * The Doctor mentions the destruction of the Earth in an alternative universe. (TV: Inferno)