And the name of Neil Gaiman's episode?
The Doctor's Wife, believe it or not.
The Doctor's Wife, interestingly, was the title of a fake story that John Nathan-Turner, the producer during the 1980s, put up on a production board in order to ferret out information leaks...
And besides the hoo-hah over the character of Idris, there's this interesting tidbit Gaiman told
Doctor Who Magazine (I copied this over from the Doctor Who News Page)...
Idris is someone who is beautiful, and who bites, and who might just turn out to be an old acquaintance with a new face... [adding] it starts in void-space, with something – or someone – we have not seen since The War Games, and a knock on the TARDIS door...
Now, there are a few characters off-hand whom I could think of. There's Jamie, perhaps, or the War Chief, but I have the feeling that Gaiman may actually be talking about Zoe Heriot...