In the turbulent Parisian summer of 1893, Victor Legris has vowed to give up the dangerous hobby of amateur sleuthing to concentrate on selling books. But a murderer is at large in Paris, intent on revenge for events that took place many years before during the Commune. And when a bookbinder friend of Victor's becomes the latest victim of the mysterious Leopard, the young bookseller feels impelled to resume his detective work and uncover the identity of the Batignolles predator.