Helen Vardon's Confession by R. Austin Freeman

Through the open door of a library, Helen Vardon hears an argument that changes her life forever. Helen's father and a man called Otway argue over missing funds in a trust one night. Otway proposes a marriage between him and Helen in exchange for his cooperation and silence. What transpires is a captivating tale of blackmail, fraud and death. Dr Thorndyke is left to piece together the clues in this enticing mystery.