I think this may be the first Christie book that I've read that was set later in her career. It was interesting to see the changes in dialogue and story line in a book first published in 1969 and those by the same author that were originally published a couple of decades or so earlier.
It was also my first meeting with Ariadne Oliver, and I adored her.
A 13-year old girl is murdered at a Halloween Party after boasting that she witnessed a murder. The girl is known to stretch the truth and therefore isn't believed by those who heard her boast. There's some talk that perhaps some mentally ill stranger snuck in and did the deed. That's definitely much better than suspecting someone else at the party--a neighbor, a friend--was responsible. Mrs. Oliver, a popular crime novelist, doesn't think so. She then enlists Poirot to investigate.
Poirot doesn't put much stock in the stranger theory, either, and thinks the child could have been murdered for her boast. In the course of his investigation he also hears several rumors and gossip around town about a forged codicil to a Will, a missing au pair, and a murdered law clerk. Is there a connection between these and the murdered girl or is are they all unrelated tragedies?
I thought I had the mystery and the killer figured out in this one, but was only partially right.