We slipped inside, into a tight space that smelt of must and stone and the dampness of ages. Holmes closed the door behind him, and I lit a candle. We stood in a hollow perhaps five feet square and seven feet tall, rough-hewn from the rock. I had expected one passage, but we found two, both just wide enough for a man’s shoulders and tall enough for Holmes to walk without being forced to duck. We took the one to the left, which began by heading north, but soon doubled back south, then north again. We were, I decided, cork-screwing upwards in the hill below New Fort, the floor of the passageway ever rising beneath our feet. Twice we came to junctions, and after debate, we took care to mark our choice with small pebbles. After the second junction, we went for five minutes or so before Holmes and I stopped almost simultaneously, sensing the way diverging from where we wanted to be. Returning to the junction, we shifted the pebbles and went on, ever climbing, until the passage came to an end at a door as broad as the outside one had been narrow.

This door, however, had no lock, merely an expanse of uneven, time-darkened wood. I pushed against it, then dug my fingernails into one of the cross-pieces and pulled, but the heavy thing did not budge. Without a word, I stepped back far enough to allow Holmes to pass, and handed him the candle.

He ran the light back and forth over the surface, looking more for signs of wear than for a trigger, but found nothing. Not until he began to search the surrounding rock did he give a grunt of triumph. Shifting the low-burning stub to his left hand, he reached up with his right forefinger to press something hidden by a rough place in the stone. There was a faint click, and the flame danced wildly and snuffed out in the sudden current of air from around the concealed door.

Holmes pressed back against the rock to allow me passage. I laid my hand against the wooden surface, which despite its weight gave way with the silent ease of oiled hinges, and felt forward with the toe of my boot for the high marble trim that had run around the toy-room floor. It was there, and moreover, the air smelt of dust and machine oil. I stepped inside, listening for motion or the sound of stifled breathing, until I was satisfied that we were alone.

I turned back to the invisible door, and breathed, “It’s clear. Could you do something to the lock so—”

“It’s done,” Holmes whispered back. The last thing we needed, should this mad mission actually succeed, would be hunting for another trick switch with an abducted maharaja on our hands.