The famous detective Hercule Poirot is vacationing on an Adriatic island. The hotel is home to the married couples Redfern, Gardner, Marshall, and a writer and millionaire. Mrs. Marshall is a former actress who married well and dislikes her stepdaughter Linda, who is also vacationing at the hotel. Arlene Marshall is found murdered on the beach, and every guest at the hotel has an alibi. At the request of the hotel owner, Daphne Castle, Poirot begins a private investigation…