The mystery of the yellow room (Literature of mystery and detection)

This novel - the classic French detective story - was written in 1907 by Gaston Leroux, once a reporter who covered the famous trials of his time. (He also wrote THE PHANTOM OF THE OPERA.) Match your wits with his rival detectives - one amateur, one professional - as they try to crack the mystery. Mademoiselle Stangerson retires to bed in the Yellow Room. Suddenly revolver shots echo through the house and she screams for help. Her father and a servant run to the locked room where they find the wounded girl - alone. The only other exit, a window - barred. How had the assailant escaped?