The Mystery of the Yellow Room

Mademoiselle Stangerson is attacked by an unknown assailant, who then escapes from her locked bedroom without being seen. Joseph Rouletabille, a bright young reporter, is drawn to investigate the mystery, trying to understand what really happened (and how ! ) before another attempt on her life is made. The Mystery of the Yellow Room is an early "locked-room mystery" novel, and helped define it as a genre.
Agatha Christie, in her novel The Clocks, had her fictional detective Hercule Poirot describe it as a masterpiece. John Dickson Carr, frequently cited as the best mystery writer specializing in locked-room mysteries, named it as his own personal favorite example of the genre.