When Herbert Wrayson, a bachelor, arrives to his apartment one night, a young woman is rummaging through his desk. When he confronts her, she claims that she was at Morris Barnes' apartment, his neighbor who lives above him. She leaves his apartment silently and makes her way to Barnes' house while he is on the phone. A few hours later, she knocks on his door once more, this time appearing frightened and weak. The corridor is dark, so she requests Wrayson's help in getting her downstairs. Morris Barnes is seated in a hansom at the doorway as they leave.But they find Barnes has been choked to death. Wrayson quickly discovers that the young woman is the elder, estranged daughter of retired Colonel Fitzmaurice, a club acquaintance. He also finds that he has fallen in love with her. But the crucial query is: Has he fallen for a murderess? How can he learn the reality? In classic Oppenheim fashion, this "whodunit" spins a complex web, and the shocking conclusion can only be found at the very end.