Poirot receives an unusual request for help from a Miss Violet Marsh, who was orphaned as a child and went to live with her peculiar Uncle Andrew. He died a month ago, leaving a will with a strange clause. Marsh has given instructions that his "clever" niece is allowed to live in his house for one month and in that time she has to "prove her wits" and find his second will. If at the end of that time she hasn't, all his worldly goods go to charitable institutions and she will be left with nothing. Can Poirot help her?