A. E. W. Mason 
The Affair at the Semiramis Hotel (Serapis Classics) [EPUB ebook] 

BOOK 2 IN THE INSPECTOR HANAUD SERIES, in which we again join Ricardo and Hanaud, this time in an ambiguous situation. A young, wealthy vagabond English man, Calladine, whom Ricardo knew before, hastily comes to Ricardo’s London home in the morning, while Hanaud happens to be visiting. Calladine, very agitated, still dressed formally as for an evening ball, tells his disturbing story– He had gone to a costume party that night in a hotel ballroom, met a beautiful young woman, Joan Carew, with whom he danced, dined, and talked…