This is the 15th book in the Hercule Poirot mysteries and the second book featuring Colonel Race. It's one of my favourite of Christie's mysteries and one of the saddest.
The very poor Simon Doyle meets the equally poor Jacqueline de Bellefort, they fall passionately in love, get engaged and Jackie introduces him to her very wealthy best friend Linnet Ridgeway - who promptly steals Simon away.
Enter Egypt, three months later, on a cruise up the Nile. The newly wed Simon and Linnet are on their unhappy honeymoon as they're pursued by a vengeful Jackie. Poirot, also on the cruise, watches the drama uneasily as he suspects things are not quite what they seem. With Linnet's murder, the theft of pearls, the appearance of Colonel Race on the trail of a foreign agent, and far too many suspects who wanted Linnet dead - Poirot finds a very confusing case that taxes his little grey cells.
I'm always saddened by Linnet's death. She was spoiled and used to getting her own way, but she was only 20 years old and to kill someone so young for money is just so meaningless. Money is an imaginary concept, without worth. Linnet shouldn't have been murdered for it, especially not with the justification that she had betrayed a friend and stolen her fiance as the slim reason behind it all. People mature, they grow out of their feckless youth. Linnet would never have the chance.
I'm still quite fond of Colonel Race. He doesn't have Poirot's skill at puzzling out the truth, but he's such a comforting character. I've liked watching him develop through Christie's novels.