Poirot visits Cornwall to attend a dinner hosted by his friend, the retired actor Sir Charles Cartwright. When an amiable local Reverend chokes to death on his cocktail Poirot cannot see how murder can have been committed. With the exception of Sir Charles's doctor friend Sir Bartholomew Strange and the enigmatic Miss Egg Lytton Gore any one of the eclectic mix of guests might have taken the glass - the inquisitive playwright, vulnerable ex-jockey, celebrated dressmaker, faithful housekeeper or young suitor of Miss Lytton Gore's. There seems to be no motive for murder and as Poirot predicts, no trace of poison is found in the Reverend's glass. But weeks later Sir Bartholomew Strange chokes to death at a dinner party he is hosting with many of the same guests. Poirot and Charles travel from Monte Carlo to Strange's home in Yorkshire where Charles is determined to solve his friend's death and to impress Egg. Again, no trace of poison is found in his glass but a mortuary report confirms that Strange was poisoned and this time motives seem plentiful. Could the missing butler, mysterious telephone message or secret tunnel be key to solving the case? It is only after the death of another innocent victim that the impossibility of the first murder begins to make sense.