How long this exchange might have continued, it is hard to say, but Holmes had clearly heard enough.

“If you do not open this door at once,” said he in a masterful tone, “we shall put the matter in the hands of the police immediately.”

For a moment there was silence, then we heard the sound of a bolt being drawn and the door was opened. The man who stood back to let us enter was one of the oddest human beings I have ever seen. He was somewhat over middle height, but strangely hunched about the shoulders, so that his neck and head protruded forward like that of a tortoise. His chest and shoulders were very stocky, but the rest of him seemed to taper away almost to nothing, ending with a pair of very small feet.

“Come in, then, if you must,” said he in an impatient tone, waving his arms at us. As we did so, there came a terrific racket from somewhere upstairs, a woman’s voice, shouting raucously, and a violent banging noise, as if someone were kicking at a door. “It’s only the maid,” said Silas irritably. “She’s probably got herself locked in the broom cupboard again. I’ll deal with it in a minute.” He closed the front door behind us, and as he did so the noise upstairs subsided. “Thank goodness for that,” said he in an unpleasant tone.

“Now,” he continued, addressing David Boldero, his head protruding forward as he did so. “You wish to speak to me of your brother. It is true, I admit, that I saw him in January, but I had good reason for denying it, as you will understand shortly. The matter is more complex than you perhaps suppose. You had best all come this way, and I will explain everything.”

He opened a door at the right-hand side of the hall and led us into a dusty, unfurnished room. A penetrating smell of damp filled the air, and plaster had fallen from the walls in chunks and lay in crumbling heaps upon the bare boards of the floor. As I closed the door behind us, I thought I heard the woman shouting again upstairs.

“You will excuse the slight disarray,” Silas remarked over his shoulder, as he led the way to a door at the far side of the room. “This room is in need of a little redecoration. This will be the quickest way,” he continued, throwing open the door and passing through it.

We followed him along a narrow flagged corridor, which ran along the right-hand side of the house and appeared to have been added as a way of getting from the front of the building to the back without passing through the inside of the house. A row of dirty, smeared windows on our right looked out over the gardens, which were as Boldero had described them: a confused mass of overgrown shrubs and tangled creepers, upon which the rain now fell steadily.

At the end of the corridor was another door, with a small rectangular pane of glass set in it near the top. Silas Boldero glanced through this, then drew back a bolt and pulled the door open.

“Come on, come on!” he said impatiently. “Let’s get out of the cold!”

We filed through the narrow doorway after him into a long, high-roofed conservatory, built on to the back of the house. The air in here was much warmer, very moist, and had an odd, unpleasant smell to it. I was the last to enter, and as I did so it was clear that our host was becoming very irritable.

“Hurry up!” he cried, putting his hand on my shoulder as I passed him at the doorway. “Let’s get this door closed!”

“Look out!” cried Holmes, but his warning came a fraction of a second too late, for at that instant I received a violent push in the middle of the back, lost my balance and stumbled into the others. In that moment of confusion, Silas Boldero slipped back through the doorway, slammed the door shut behind him, and shot the bolt home. A moment later we heard his rapid footsteps ringing on the flagstones of the corridor. Above us the rain drummed heavily on the glass roof of the conservatory, so that we had to shout to make ourselves heard.

“What the devil is going on!” cried Boldero in an angry tone.

“We have been tricked,” said Holmes, his keen eyes darting round the strange structure in which we found ourselves. It had been built against the wall of the house, so that on our left was a tall blank wall of brick. Incongruously placed high up in this wall, directly above where we stood, but with no way of reaching it, was an ordinary-looking door.

“That must be the door through which I fell last night,” said Boldero, following my gaze. From the house wall, the roof of the conservatory sloped down steeply to a lower wall, on our right, which was composed entirely of glass panels. At the near end of this wall was a pair of doors of similar construction, which gave onto the garden. A quick examination showed that these doors were locked.

But though I quickly took in all these features of the building, it was the floor that arrested my attention. Where we stood it was composed of large square flagstones, moss-covered and slimy, which extended for about twenty feet. Beyond that, the floor sloped gently downwards, into what appeared to be a deep bathing pool, which extended for a further thirty or forty feet, to the far end of the building. The surface of the water was green-skimmed and unhealthy-looking, and covered with drifting vegetation and other debris. Even as I looked, however, I saw something moving there, a purposeful dark shape beneath the water.

“Holmes!” I cried, but he had already seen it and his keen face was rigid with tension. Whatever it was, it was moving up the pool towards us, its swift, gliding motion sending little ripples out as it approached. Then, above the slime on the surface of the water, I saw the front of its snout, two large nostrils dilated to suck in air, and, some way behind, two large, evil eyes, fixed steadily upon us.

“My God!” cried Boldero in terror. “What in Heaven’s name is it?”

“It appears to be an African crocodile,” responded Holmes quietly in a voice that was icy cold. “The largest and most deadly reptile on earth. It is a monster of the species, too: it looks a good eighteen feet in length.”

As we watched, the creature slowed and then stopped altogether, lying still in the water barely ten feet from the edge of the pool, its unblinking eyes watching our every movement. Whether this quiet observation represented mere curiosity or was the prelude to a sudden assault, it was impossible to tell.

Without turning his head, or taking his eyes from this awesome vision, Holmes reached into his pocket and drew out a pistol, which he passed to me, pressing it firmly into my hand. “It may be utterly useless against such a beast, but we have nothing else,” said he softly. “If it moves any closer, Watson, shoot to kill! Now, quickly, Boldero, help me! We must try to break down the doors!”

Behind us, on the flagstones, stood a low wooden bench. Holmes seized hold of one end, but Boldero had been struck rigid with fear at the sight of the terrible creature and did not move.

“Boldero!” cried Holmes again in an urgent tone. “For your life, man!”

At that moment there came a crash above us, as that singular door high up in the wall was flung open. Framed in the doorway stood Silas Boldero, and from his hand hung a large canvas sack. For a moment he looked down upon us in silence, a horrible sneering smile upon his face, then he laughed harshly and drew from the sack what appeared to be a large piece of raw meat. With a careless movement of his arm, he flung it out into the air, and it fell with a splash in the shallow edge of the pool. The creature in the water made no discernible movement, and yet I had the disturbing impression that it had drifted very slightly nearer to where I stood.

The sudden appearance of his cousin at least had the effect of breaking the spell of fear that had held David Boldero motionless. Now he quickly bent his strength to the wooden bench that Holmes was lifting, and the two of them charged with it at the garden doors of the conservatory. With a terrific crash of breaking glass and a splintering of wood, the lock gave way, the doors flew open and the colder air of the garden rushed into the building. For a split second, as the doors were burst open, I had taken my eyes off the monster in the water, but now I saw, to my horror, that it was moving smoothly and swiftly forward, its long scaly tail thrashing the water behind it.