London, 1813. The brutalized body of a boy is found dumped into a makeshift grave on the grounds of an abandoned factory-- and his younger sister is still missing. Few in authority care about a street urchin's fate, but Sebastian St. Cyr is drawn into a shadowy, sadistic world. As he follows a grim trail that leads from the writings of the debauched Marquis de Sade to the city's most notorious brothels, he comes to a horrifying realization: someone from society's upper echelon is preying upon the city's most vulnerable.