Just as his holiday on the island of Rhodes is coming to an end, Hercule Poirot finds himself investigating a murder when one of the hotel guests, Valentine Chantry, is poisoned in the bar. The drink she had was apparently meant for her husband and had been bought by Douglas Gold, with whom she had been carrying on since her arrival. Gold is arrested and everyone assumes he is the perpetrator but Poirot thinks otherwise however and looks to the other guests in the hotel as more likely suspects. When a local pathologist confirms that the poison used was local in origin, Poirot realizes that only when he learns who purchased the poison will he learn the killer's identity.