I really enjoyed this, I read it almost in one sitting. The story mainly consists of two parts: first you have the explanation of how other worlds & doors work, introducing the characters that went there as well. The other part is a murder mystery, corpses start showing up at the school. There is a killer in their midst, the question is who it is. I explicitly say 'two parts', as I felt that as soon as the murder mystery began, there was less attention for exploring the effects of not being able to return to the world you now call home. The characters still kept mentioning how they wanted to go back to their worlds, but there was not really any progress in that story line. I expected them to try to find ways to go back, to grieve, or to try and fit into the 'normal' world more and more. This wasn't really the case, but it also has to do with the fact that this is quite a short read. 
 Overal I really enjoyed it. I love the theme of 'wayward children', exploring what happens after the fairy tale usually ends. The execution of this concept, thankfully, didn't lack. I just wanted a little bit..more?