I'll agree with the person down below who says that the title is fairly clever . . . I didn't even know that "de-montage" was a real word until this book, which just goes to show you that it's always possible to learn from anything, no matter what the source.
Granted, it would have been nice to have some actual demons in this story, given the title but I don't want to come across as being overly nit-picky. I actually would like to comment about the cover before we go too much further . . . most of the covers for the BBC line have been fairly standard, nothing much to write home about. This one at first glance makes you think you're in for a werewolf story of sorts until you look closer at it and realize that the cover isn't the Doctor, but a painting of the Doctor with claw marks in it. Nice use of detail and good use of an otherwise bored looking Paul McGann.
Meanwhile, back to the story. In a rare light hearted moment for the TARDIS crew, the team stops off on a casino world while Fitz and the Doctor indulge in a bet to see who can make the most money over the course of a week. Which already shows the changing dynamic between the crew members . . . while the Doctor would often take Sam places to show her stuff, it was rarely for something so whimsical. It's a subtle touch, even as the story gets some comedy moments out of the fact that as good as Fitz might think he is, Sam's got a few years of travelling and evading danger under her belt, while all he wants is a good cigarette.
Of course, this is not the entire plot or else whimsical would turn into boring really quickly. The casino is set in a neutral zone between people and the Canvines, a race of dog-like aliens. There was war once but now an uneasy peace has settled in, even if not everyone is thrilled over that. This is all very nice until there's a murder on the station, with one good witness who disappears. Meanwhile an assassin appears to be stalking the corridors and what does this all have to do with the art exhibition that's opening up?
Richards' has all the elements in place for a good story and it's to his credit that it reads as quite assured. There's not really a misstep or a false note, the setting is well thought out and he enjoys throwing the occasional curveball at the reader, such as making the Canvines opera lovers and not really all that war-like. I don't know if he's really all that good at conveying exactly what makes Martinique the artist so awesome but maybe he's just making fun of how pretentious it all seems. People get killed or almost get killed, there's twists as we go along and it all ends rather nicely.
Thing is, it's not terribly exciting. I mean, it's entertaining enough but it lacks a certain kind of spark. Maybe because of all the secondary characters, while he does a good job of filling the world with enough people that it doesn't feel like a four person stage play but many of them just aren't very memorable. When people vanish for thirty pages and I have to remind myself who they are when they reappear (in a book I read in like three days) that probably isn't a good sign. So this hamstrings the book slightly and while it doesn't wreck it, it tends to hold it down to "good" as opposed to "great". It doesn't help that a few of the subplots seem just there to kill time and aren't all that compelling.
The ending is a bit dodgy too, with someone you thought was dead coming back and then not doing all that much except to explain all the bits of the plot that nobody has figured out yet with a final twist that seems to be missing a few links in the logic chain.
But, as I said, none of this really sinks the story thanks to Richards' ability to keep the plot moving. You may not be able to remember any of the characters when the book is over but at least something tends to be happening on nearly every page. What could have potentially been awesome gets downgraded to "merely pleasant". Like a replica of a fine painting, it has all the components of greatness but it's just not quite there.