The Circular Staircase

Twenty-year-old Halsey and 24-year-old Gertrude, nephew and niece of Rachel Inness, a well-to-do middle-aged spinster, talk Rachel into renting a large country house for the summer. Mysterious happenings occur the first night they are there, something or someone falls down the stairs in the middle of the night. A man is dead at the foot of the circular staircase. Now the question arises as to who he is and why was he in the house. Could it have something to do with the valuables hidden in the house that are unknown by the new tenants?