Mark Ablett is entertaining a house party at his English country house. The guest list includes a widow and her marriageable daughter, a retired major, a willful actress, and Bill Beverley, a young man about town. When Mark's long-lost brother Robert, the black sheep of the family, arrives from Australia, things do not go as per plans and shortly thereafter Robert is found shot dead. Now it is up to Tony Gillingham and his friend Bill to figure out the locked room mystery and catch the murderer.