I really enjoyed this book. The setting of the children's Hallowe'en party very effectively created atmosphere right from the beginning, and the mystery had me hooked. 

I guessed part of the mystery correctly but other parts surprised me and the final reveal was a shock. It all held up in hindsight though and I could see where the hints had been throughout the book. 

Despite one or two things I wasn't keen on, which I won't spoil, I think this is one of the best Agatha Christie books I've read to date and I had a really good time with it.