Why are they disappear

The book we got to talk about is "4:50 From Paddington" written by Christie, Agatha. The book I was using was published by New American Library. The book's first publishing date is November 4, 1957. This book was talking about homicide is really miraculous homicide, because our sufferer and murder disappear, and our main chapter Miss Marple and her friends find out it have a relation with a really rich family. In this family everyone has their own secret.