This was a very short book (Novella? Bookella?) in the Discworld universe, featuring Rincewind. My Kindle edition said it was 149 pages, and it felt even shorter. Apparently it was originally published with illustrations, but I read a non-illustrated version. People had told me the illustrations weren’t necessary to the story, and I agree with them. It was perfectly coherent on its own. Well, as coherent as the Discworld ever is, I guess. :)
The basic story is that Rincewind, for reasons not worth trying to explain, finds himself unwillingly playing the role of demon for a teenage boy. There really wasn’t much to the plot, although the explanation for everything that happened was somewhat amusing. The book was cute, with some funny moments, but I don’t think it will prove to be particularly memorable.