At the fourth meeting of the Tuesday Night Club, the painter Joyce Lemprière presents her mystery. During a holiday in which she was working on one of his paintings, she accidentally painted drops of blood on the pavement. Within a few minutes, the blood was gone. Joyce later learned that a woman had drowned after suffering a severe blow to the head. The group must discover if the blood was just was just a trick of Joyce's imagination and if the death was accidental or premeditated.