When this was published Christie had already been a best-selling author for more than three decades. She's got it down. Certainly she has fun with the format. Hercule Poirot doesn't appear, isn't even mentioned, until the final act. The girl's school setting is fun: it gives her rein to use all the stereotypes and to demolish them.
This particular book was on Natasha's shelf, which is why I didn't get to it during my Christie run. Saturday night she comes to tell me goodnight and to ask if I know why the book is there. And even though I can't remember what day it is, I was able to tell her that she picked it out at a library book sale, because she recognized the author. Alternatively, every bookcase is required to have at least one Christie. Or, maybe, a book is just a clever disguise for aliens who've come to observe us. After two hours of increasingly random speculation about space, and teleportation, and replicators, she finally went off to bed, leaving the book with me, because now it felt slightly sinister.
Subtle evil plan to acquire all the books is working. "Maniacal laugh, maniacal laugh, maniacal laugh." Personal copy now.