Death on the Nile by Agatha Christie, Mallory (DM)

Linnet Doyle is young, beautiful, and rich. She's the girl who has everything--including the man her best friend loves. Linnet and her new husband take a cruise on the Nile, where they meet the brilliant detective Hercule Poirot. It should be an idyllic trip, yet Poirot has a vague, uneasy feeling that something is dangerously amiss.