Quick recap
Heiress Linnet Ridgeway hires Simon Doyle, fiancé of her friend Jackie de Bellefort, and ends up marrying him. On their Egyptian honeymoon, Jackie follows them onto the steamer Karnak, where Poirot is also a passenger. One night, drunk, she shoots Simon in the leg. The next morning Linnet is found dead, but Jackie spent the night under watch. The maid Louise and novelist Salome Otterbourne die too. Poirot gathers everyone in the saloon: Simon and Jackie were still lovers. The shooting was staged, Simon killed Linnet and then really wounded himself, and Jackie silenced the witnesses. Caught, she shoots Simon and then herself.

