Amelia Barrowby is in fear for her life, fearing someone in her home will kill her. When she sees Poirot at a flower show where he is receiving an award, she speaks to him for a moment, giving him a packet of flower seeds. When he arrives back at his office, he discovers the seed packet is empty, and a letter from Mrs. Barrowby arrived in the morning post, which he did not receive on time. He follows up on the letter the next morning, but discovers he is too late--Mrs. Barrowby is dead, poisoned with strychnine. Mrs. Barrowby's will leaves everything to her Russian nurse, who is suspected of the poisoning, both by inspector Japp and Mrs. Barrowby's live-in niece and her niece's drunkard husband. But did the nurse commit the murder, and if so, why?