Wow. Now this here is some serious fanwank. It makes sense, don't get me wrong, but it's wanky.
On the one hand, we have the Doctor off doing he-knows-what, his absence more of an annoyance than a chance for Benny and Ace to stretch their legs. One of the annoying parts of the novel was how very often the women go off on inner rants about this. Not that they aren't entitled, but I found myself skipping paragraphs. It felt as if the author noticed the book was coming in short and padded it with grumps about what a manipulative shit Seven is.
And good lady, the timey-wimey got thick. I've knitted cable scarves with fewer twists in them. I could have enjoyed it more if there had been fewer clearly-Doctor-dropped clues. As it was, every time Benny got into a rhythm of her own, there was another drop (and another rant, of course). At least Ace got to do some organizing and figuring out of her own, a talent I wish was used for more than military purposes.
Now the big gripe: I hope we don't see the TARDIS have to expel someone/thing again soon. I really got my fill of that over the first seven books, and here we are again. It starts to feel like that's what excited the editor more than anything: watching the rape of the TARDIS. That's what it is, and it is becoming seriously uncomfortable. All the virus metaphors in the world can't obscure it by now, especially in a novel of what is essentially sisterhood.
The plot worked, and it was much better in its take on the East End than the joke that was "The Pit." It did try hard. Ultimately, though, this was a novella that got overexpanded.