'Interference (Book One)', written by Lawerence Miles, features the Third Doctor, Eighth Doctor, Sarah Jane Smith, Sam, and Fitz Kreiner.
Back Cover Blurb
They call it the Dead Frontier. It's as far from home as the human race ever went, the planet where mankind dumped the waste of its thousands year empire and left its culture out in the sun to rot.
But while one Doctor faces both his past and his future on the Frontire, another finds himself on Earth in 1996, where the seeds of the empire are only just being sown. The past is meeting the present, casue is meeting effect, and the TARDIS crew is about to be caught in the crossfire.
The Third Doctor. The Eighth Doctor. Sam. Fitz. Sarah Jane Smith. Soon, one of them will be dead; one of them will belong to the enemy; and oneof them will be something less than human.