The Golden Age reading challenge I've been doing this year has been jumping forward and back in time – it’s read the first six Poirot books and the first six Miss Marple books, in alternate months. But when Christie wrote this fifth Poirot novel, she still hadn’t written her first Miss Marple novel. The Murder at the Vicarage was not published until 1930. Last month’s Miss Marple, Sleeping Murder, was set in 1944, but we’ve now returned to the glamour of the Roaring 20s in The Mystery of the Blue Train. This jumping back and forth in time does give us the first reference to St Mary Mead, the fictional English village where Miss Marple would live, before we even meet Miss Marple. Katherine Grey, our main character here, is from St Mary Mead. At one point she receives a letter from someone at home which refers to “great trouble about the new curate, who is scandalously high. In my view, he is neither more nor less than a Roman”. In The Murder at the Vicarage the village is still outraged by the popish tendencies of the new curate.

The Mystery of the Blue Train is Christie’s least favourite of her stories. She struggled to write it before and after her disappearance in 1926. In her autobiography Christie stated that she “always hated it”. However, she also says of it that this was the moment she changed from being an amateur writer to a professional, when she had to “write even when you don’t want to, don’t much like what you are writing, and aren’t writing particularly well”. But despite this, it’s not that bad a mystery and it sold well for her. Christie took the bare bones of the plot from a short story she published in 1923 - The Plymouth Express (you can find this story in the short story collection Poirot’s Early Cases) and expanded the central idea into a full-length novel. Spoiler alert - if you read the short story ahead of reading this novel, there are some plot elements that remain the same, and sections of the book that are lifted directly from the short story, such as the evidence the maid gives. This was a reread for me, so while I didn't recall every detail, I remembered enough to realise early who the murderer was. And I reread the short story immediately ahead of starting it, so I had the similarities in my head as I read. Christie also reused another short story late in the book. There is a chapter near the end where Poirot meets a friend at a restaurant. The initial dialogue between them is lifted straight from the opening of Four and Twenty Blackbirds.

Katherine Grey has spent the last ten years working as the companion to a difficult old lady, Mrs Harfield. She is surprised to learn on Mrs Harfield’s death that she is the old lady’s sole heir, and is even more surprised to learn that Mrs Harfield was an extremely wealthy woman, despite living fairly simply. Katherine decides that she would like to travel, and accepts an invitation from a distant relative to spend winter with them on the French Riviera.

Katherine travels on the luxurious Blue Train, joining other wealthy travellers who also intend to have a season in the sun. On the train she meets Ruth Kettering, the only child of the American millionaire Rufus Van Aldin. Ruth is in the process of divorcing her philandering husband, Derek, while simultaneously conducting a discrete affair with the Comte de la Roche. Ruth has with her a fabulous ruby, the Heart of Fire, a recent gift from her indulgent father. Other passengers on the train are Derek (Ruth’s estranged husband), Mirelle, a beautiful, infamous dancer and paramour of Derek, and Hercule Poirot.

From the opening we see that the story has a range of classic mystery elements - a fabulous jewel with a dark history (to paraphrase Sherlock Holmes in The Adventure of the Blue Carbuncle, all good stones are the nucleus and focus of crime), a master criminal/jewel thief, heiresses, luxury trains, exotic lovers and wronged spouses. When the train arrives in Nice the next morning, we get the last thing we need for a murder mystery – Ruth Kettering’s body is found in her cabin. She has been strangled. The rubies are missing. Naturally Poirot becomes involved in the investigation, even though he is ostensibly retired. He just can’t resist putting his oars in at first, then Van Aldin hires him to find his daughter’s murderer. And Katherine becomes involved too, partly because she spoke to Ruth on the train so she is an important witness, and partly because Katherine also met Poirot on the train. They were seated together at dinner. Katherine has a mystery novel with her that Poirot comments on, and he promises her that one day they will investigate a real mystery together.

The cast of suspects is small. This appears to be classic closed circle mystery set-up. There are two obvious suspects to the murder who are the focus of the police investigation. One is arrested, but Poirot is not satisfied with that person’s guilt, and manages to break the alibi of the other suspect. But that still isn’t the end. Poirot keeps investigating, and finally gives a solution that seems to come out of nowhere. But, if you read carefully, there are a few good hints included along the way. Admittedly, I may not have spotted them if I hadn’t read the book before. I probably didn't spot them on my first read, because the only Christie novel I have ever managed to solve is Peril at End House.

Overall, I think Christie judged her book too harshly, although that is understandable given the turmoil in her life when she wrote it. It’s a clever mystery with a clever solution. Of course, I have a bias with the setting of the murder: the thought of taking a long journey on a luxury train is something that appeals to me. The Blue Train sadly no longer runs, but I'd settle for a trip on the Orient Express, or even on the Ghan (an Australian train that runs between Darwin and Adelaide). If you like classic mysteries, I think this one is worth reading.