This book was published in 1928 and is an expansion of the short story "Mystery of the Plymouth Express". The plot enters around an American heiress, her millionaire father, ne'er do-well husband, shady lover and others she comes into contact with on the famous Blue Train while traveling to the Riveria. The question becomes was she murdered for her jewels or were her jewels taken to cloud the motive of her murder? Katherine Grey (from the soon to be famous St. Mary Mead) was taken into the victims confidence and finds herself entangled in the mystery. Fortunately for her, Hercule Poirot was also a passenger on the train and sorts through the puzzle. Poirot is traveling without Hastings but we are treated to scenes with Georges the valet at the beginning of his career with Hercule.
This book has held up surprisingly well considering it is nearing the century mark. It describes a way of life that is long past which could be confusing the 21st century reader who does not understand the stigma that had been attached to divorce, limited opportunities for women or personal servants but the core conflicts of the story remain current to today.
The only flaws I see in this story are the number of subplots and secondary characters but this is more than made up for by the ending which has the typical Christie flair.