The Algebra of Ice (novel)

 was the sixty-sixth novel in the BBC Past Doctor Adventures series. It was written by Lloyd Rose, released 6 November 2004 and featured the Seventh Doctor, Ace and Brigadier 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

Worldbuilding

 * Paul Erdős is considered to be "the last of the great abstract thinkers".

Foods and beverages

 * The Doctor drinks orange juice and serves buttered toast and honey to Ace and Ethan for breakfast.
 * Ace drinks hot chocolate. She also likes beer and gets drunk here.
 * The Brigadier starts the day with coffee.
 * The food machine makes Bourneville Fruit and Nut bars on demand.

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)
 * The Brigadier is familiar with Seventh Doctor and Ace is familiar with the Brigadier. Ace refers to UNIT taking unnamed individuals to a secret prison and she presumes they are still there, a likely reference to Morgaine and Mordred. (TV: Battlefield) Ace also mentions Fenric. (TV: The Curse of Fenric)
 * These details place this novel during or after 1997. (PROSE: The Dying Days)
 * 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)