Holmes nodded. “I thought as much, the first time he came to my cell. But if a passageway links the Old Fort with the New, that would still require passing a number of guards. Unless it also has an opening to the outside.”

I sat up as if brushed by a raw wire. “The zoo!” The three men looked at me. “When the maharaja showed us the zoo, I noticed a small pathway going around the back of the lion pen, past the entrance used by the zookeepers. The big path was marked heavily by bits of spilt food and the drag of equipment, but beyond it was the sort of footpath worn by a single set of feet, walking it with regularity. His dogs knew it as well—when they would have gone down it, he called them back. Sharply.”

“That could be anything,” Nesbit objected.

“I think not. The lion pen itself is built right up against the hill of the Fort, firmly into its westernmost side. And just before going to the zoo, I was in a room in New Fort located on the heights of that same side. The toy room, he calls it. Have you seen it?” I asked Nesbit.

“Years ago, and briefly. But you’re right, it is on the western spur of the New Fort.”

“It has a hidden door. I noticed the wear on the floor there, where the marble is grey with soil and scattered particles of gravel. The servants do not clean in the toy room very often. And in fact,” I said as another piece of the puzzle came to me, “the maharaja has the reputation of sorcery—of being able to appear and disappear unexpectedly. No doubt this is partly explained by the number of purdah screens throughout the Fort, which would conceal a small elephant, but there may be a network of hidden passages as well. And you’d expect one to the outside, such as down to the zoo.

“Too,” I said before they could object, “there may be a similar hidden passage in that horrid fur-lined gun-room of his. A room which is near the gates on the east side, a location which would be very convenient for crossing under the road to the Old Fort in the night. A passageway smelling of stones and dampness.”

Silence again fell in the room, but it was an electric silence of intense speculation rather than repose. Even the boy was awake—or had given up the pretence of sleep—and had drawn himself up at his father’s side.

“Provocative,” Holmes said at last, and proceeded to repack his borrowed pipe with the Indian black leaf.

“You’re certain?” Nesbit demanded.

“Of soil and wear on the floor near two blank walls? Yes. That those doors lead to the zoo and the Old Fort? Of course I cannot be sure.”