The lions’ pen would have been easy for a blind person to locate, stinking of carnivore, the faint splash of water from the hillside spring the only noise in the great stillness. Our boots made no sound on the winter-soft grass, our clothing gave less rustle than the breeze in the leaves. We drew near the high, gleaming bars, the trees and rock wall behind them a dapple of light and dark.

Then a lion roared from what seemed ten feet away, and I nearly screamed in response. We froze, and my heart coursed and leapt in my chest, making me dizzy; the night seemed to pulse and fade. There came the sound of a large body shifting, the pad of enormous feet, and a second roar. We remained motionless. Would a night watchman come to investigate? Did the roar of lions mean the same as the bark of a dog? Or was the animal merely calling into the night, in hopes that his voice might be heard by another?

After an interminable time, which was probably only six or eight minutes, the animal grunted to itself and padded across the ground. Then it dropped with a breathy grunt and quieted.

I began to breathe again. After a minute, one of the men touched my arm, and we crept forward, cautious as mice in a cattery.

At the end of the lion cage, the greenery closed in so it became impossible to avoid the gravel, but when I gingerly set my foot onto its pale surface, I found that here it had not been refreshed as recently as in the centre of the zoo, and the stones in this damp place had sunk into the ground. We passed the door to the keeper’s building behind the cage where the food and cleaning equipment was stored, and where the white gravel came to an end.

But as I had remembered, there was an unnatural space between the bushes and the building where the salukis had bounded as at a familiar way, and the ground under our feet bore the unmistakable imprint of traffic. Working by feel alone, unable to see anything but the glow of the sky above, I patted my way along the walls until I came to the place where baked-mud wall merged with the naked rock of the hillside.

There we found the door. Unevenly shaped to suit the rough wall, too low for even a short man to pass while standing, and narrow enough to require slipping through sideways.

And locked.

Holmes eased past me to deal with that little problem, and when his pick-locks had done their work, we all breathed a sigh of relief to find the door unbarred. A battering-ram would not have suited our purposes at all.