What to read after Murder in Mesopotamia?

At the request of archaeologist Dr. Eric Leidner, Amy Leatheran has accepted a position as companion to his wife, Louise, a woman prone to "nervous terrors"--And in need of a confidante. She's found one in Amy. But what is the young nurse to make of Mrs. Leidner's bizarre stories of her first husband, a dead German spy, who has returned in a rage to destroy her new marriage? Stories of terrible threats and dreadful warnings? Stories that everyone attributes to a vivid--and disturbed--imagination? Yet it's more than a flight of fancy that bludgeons poor Mrs. Leidner to death. And it's going to take the brilliant imagination of Hercule Poirot to unravel the strange facts in a dead woman's fantasy.