'Independence Day', written by Peter Darvill-Evans, features the Seventh Doctor and Ace.
Back Cover Blurb
'Danger is my middle name,' Ace said, 'or it would be if I had more than one. I can look after myself these days, you know.'
Freedom. Liberty. Free will. Independence. Choice. Everyone wants to be free. But at what point does freedom become irresponsibility? What happens when one person's choice causes another's oppression?
The Doctor's on a simple mission to return a communications device he borrowed years previously. Being a Time Lord, he can return it before anyone misses it.
But events in the Mendeb system have moved more quickly than the Doctor estimated, and he lands in teh ruins of a civilisation devastated by mysterious invaders.