Book. Though probably expensive. Adventuress is like fifty quid now, and she’s not in it. I think her first appearance...sort of...was in Paul Cornell’s one with the brigadier and something like Morgaine World from battlefield. Harrier jets fighting dragons.
Looked it up...sort of..one part memory to one part poking around on kindle store. Shadows Of Avalon...I believe that’s the one where Compassion is born. More or less. Six quid on the UK store. For about four quid you can get the first volume of i’ Who which is a sort of potted set of synopsises and analysis of a huge chunk of the Doctor Who novels, and something I read back in the day to figure out which ones to get my hands on (I came lateish to the EDA party, having drifted off during the NAs then found a load cheap in a discount store. To this day I pine for a complete set, or at the very least some of the important ones I missed...stuff with Dark Sam and most of the Sabbath Arc. The time war stuff in there and the NAs was so interesting, and so blatantly lifted from for the on screen version, even if it’s not the same war...officially.)
Some of the books - Larry Miles's ones I think - suggest pretty clearly that the Master's TARDIS, Lilith, is evil, and she pushed him across from iffy to outright bad. This is all pre-Sound of Drums, etc, of course.