This book is clearly thoroughly-researched. I have no idea if it's accurate or not because the Aztec mythos is not my specialty, but if it's not accurate it holds together as cleanly as reality does. Tenochtitlan is a tangible place in Orman's capable hands. The Doctor's love for the place and its people - odd as it might seem to his companions - shines through.
The characters are plausible. The enemy is menacing and really terrifying - where we've been just told to accept some of the enemies as dangerous, boy howdy this one is believably nasty. More important, this is the first book since White Darkness where I really, really like Benny. She is scared and overwhelmed and when she thinks about jumping ship, it's clear this is not just a feeling-sorry-for-herself moment. Anyone would feel the same in those circumstances.
Best of all and thank goodness, Ace isn't falling into bed with anyone. I cannot express how happy this makes me. Orman has a fantastic feeling for Ace's natural speech rhythm and how a grown Ace would sound, and instead of Ace being a soldier paper doll she's a real person again. It gives it even more impact when the baddie does what he does to her, and makes it even more poignant that the Doctor elects not to tell her what she did.
The Doctor makes mistakes, and bad ones - but he doesn't come across as blind to the implications of the chances he takes. He does figure out what's going on in time to save the day, and he nearly loses himself in the process.
The plot uncoils itself very neatly, with a minimum of missteps. Christian is a sympathetic character, and his bundle of blankets and its passenger in the end are wonderful. He is intensely human and I like him as well.
The best thing about the book is the cleanness of the prose. Everything is clearly described. Orman doesn't try to keep her words to small syllables. She has faith in the reader, and as a result the book just flows. She assumes that the reader loves Who as much as she does, and that love carries the characterization through hard scenes.
I cannot recommend this book highly enough.