The backstage drama at the Metropolitan Opera often rivals the onstage performances, but generally doesn't prove fatal. Not so for prompter Rudolf Salz, who chose a most inopportune moment during the second act of Wagner's Die Walküre to die of strychnine poisoning—directly in view of the star of the opera, Elsa Vaughn. Not surprisingly, she misses a note or two. When Detective-Lieutenant Sam Quentin arrives on the scene, he learns that the poison was in a bottle of scotch whiskey pilfered from Miss Vaughn's dressing room. Was she the intended victim? Was this all the work of her understudy, the very ambitious Miss Hilda Semple? Or was the poison truly intended for Salz, an embittered former Wagnerian tenor, once world-famous, and now reduced to coaching other singers? When a second murder takes place, Vaughn can no longer deny that she may be a target.