'Timewyrm: Apocalypse', written by Nigel Robinson, features the Seventh Doctor and Ace.
Back Cover Blurb
The end of the Universe. The end of everything.
The TARDIS has tracked the Timewyrm to the edge of the Universe and the end of time - to the lush planet Kirith, a paradise inhabited by a physically perfect race.
Ace is not impressed. Kirith has all the appeal of a wet weekend in Margate, and its inhabitants look like third-rate Aussie soap stars.
The Doctor is trobled, too: if the Timwyrm is here, why can't he find her? Why have the elite Panjistri lied consistently to the Kirithans they govern? And is it possible that the castastrophe that he feels impending is the result of his own past actions?