Aunt Ray Innes leases Sunnyside House, the country home of Paul Armstrong, and invites her nephew and niece, Halsey and Gertrude Innes. En route, the young people stop at the Greenwood Club to take Jack Bailey, the intended husband of Gertrude and cashier of the Armstrong Bank. Halsey appears in time to prevent a fight between Jack and Arnold Armstrong, son of the banker. At three o'clock in the morning a pistol shot awakens Aunt Ray, who summons her servant, Liddy. They are joined by Gertrude, and the women discover that Halsey and Jack are missing. Investigations disclose the lifeless body of Arnold Armstrong lying at the foot of the circular staircase. Mr. Jarvis, who had been summoned from the club, recalls that Jack and Arnold were bitter enemies because of banking affairs. The next morning Mrs. Watson, the housekeeper, appears suffering from an injured arm, which she explains she sustained in falling down the circular staircase