And Then There Were 7: Hallowe'en Party by Agatha Christie

"It's Hallowe'en! It's Hallowe'en! The moon is full and bright! And
we shall see what can't be seen on any other night!" Which in a
Christie novel means a child murder, lots of velvet trousers, an
extended argument between M. Poirot and Mrs. Oliver about form
versus function, and an unexpected nod toward the holiday's pagan
origins. And SO much more. Come celebrate this spookiest of
holidays with us... IF YOU DARE.