Paris, of course.

The tunnels were dark and foul, piled with the remains of Paris' ancient dead. These particular catacombs appeared on no map and were visited by no tourists or civic inspectors. William's guide--a hunchbacked man with only one good eye--assured him they led precisely where he wanted to go: beneath the Paris Opera House.

Bones crunched under William's feet. The hunchback carried a smoking torch, which he now pushed into William's hands. "Je n'irai pas plus loin," he said. William grunted, taking the torch and thrusting the man's payment into his stubby hand. The bent little man turned and ran off into the darkness, but not before calling out, in strained English: "Give up on this. It will mean ****." But William was already forging on ahead. The inky shadows seem to cling to him. How much further could it be? There was only--

He saw the chord an instant before it snapped tight around his neck, and he managed to slide the tips of his fingers between it and his throat. The strangler's wire bit into his flesh and he was yanked off his feet. Something dragged William through the dark and filth of the tunnel, and when he looked up again he found a man in refined but tattered eveningwear and a strange, bone-white mask looming over him, the end of the noose in one hand, a long knife in the other. "A visitor," the masked man said. "What business here could have been urgent enough that you would walk so blithely into the jaws of ****?"

William bit his tongue. Whatever he said next, it would have to be good...