A lot of what makes this book so great is its mystery, so I don’t want to say too much. I will say that it’s set in the tenth Doctor specials era, probably immediately before or after Waters of Mars, and the Doctor is not well. I basically read this in one sitting. There's no companion for the Doctor to really bounce off of for a lot of this book, so we spend a lot of time just in his head, and boy is it a mess in there (in the most interesting possible way). Highly recommend.