Quick recap
Miss Marple goes to Stonygates, the mansion of Carrie Louise, an old school friend's sister. Her third husband, Lewis Serrocold, has turned part of the house into a center for young delinquents. A surprise visit from Christian Gulbrandsen, who runs the family trust, puts everyone on edge. One night, the troubled Edgar Lawson locks himself in the study with Lewis and fires a gun. While everyone stares at that door, Christian is shot dead in another room. Then two more people die in the house's little theater. Miss Marple spots the stage trick: Edgar was faking madness and imitating Lewis's voice, while Lewis ran along the terrace to kill Christian and cover up his embezzlement. In the end, both drown in the lake.
No spoilersOpens once you mark the title as seen.