I looked at my watch. It wanted five minutes to twelve, when the premonitory symptoms of the working of the laudanum first showed themselves to me.

At this time, no unpractised eyes would have detected any change in him. But, as the minutes of the new morning wore away, the swiftly-subtle progress of the influence began to show itself more plainly. The sublime intoxication of opium gleamed in his eyes; the dew of a stealthy perspiration began to glisten on his face. In five minutes more, the talk which he still kept up with me, failed in coherence. He held steadily to the subject of the Diamond; but he ceased to complete his sentences. A little later, the sentences dropped to single words. Then, there was an interval of silence. Then, he sat up in bed. Then, still busy with the subject of the Diamond, he began to talk again - not to me, but to himself. That change told me that the first stage in the experiment was reached. The stimulant influence of the opium had got him.

The time, now, was twenty-three minutes past twelve. The next half hour, at most, would decide the question of whether he would, or would not, get up from his bed, and leave the room.

In the breathless interest of watching him - in the unutterable triumph of seeing the first result of the experiment declare itself in the manner, and nearly at the time, which I had anticipated - I had utterly forgotten the two companions of my night vigil. Looking towards them now, I saw the Law (as represented by Mr. Bruff's papers) lying unheeded on the floor. Mr. Bruff himself was looking eagerly through a crevice left in the imperfectly-drawn curtains of the bed. And Betteredge, oblivious of all respect for social distinctions, was peeping over Mr. Bruff's shoulder.

They both started back, on finding that I was looking at them, like two boys caught out by their schoolmaster in a fault. I signed to them to take off their boots quietly, as I was taking off mine. If Mr. Blake gave us the chance of following him, it was vitally necessary to follow him without noise.

Ten minutes passed - and nothing happened. Then, he suddenly threw the bed-clothes off him. He put one leg out of bed. He waited.

"I wish I had never taken it out of the bank," he said to himself. "It was safe in the bank."

My heart throbbed fast; the pulses at my temples beat furiously. The doubt about the safety of the Diamond was, once more, the dominant impression in his brain! On that one pivot, the whole success of the experiment turned. The prospect thus suddenly opened before me was too much for my shattered nerves. I was obliged to look away from him - or I should have lost my self-control.

There was another interval of silence.

When I could trust myself to look back at him he was out of his bed, standing erect at the side of it. The pupils of his eyes were now contracted; his eyeballs gleamed in the light of the candle as he moved his head slowly to and fro. He was thinking; he was doubting - he spoke again.

"How do I know?" he said. "The Indians may be hidden in the house."

He stopped, and walked slowly to the other end of the room. He turned - waited - came back to the bed.

"It's not even locked up," he went on. "It's in the drawer of her cabinet. And the drawer doesn't lock."

He sat down on the side of the bed. "Anybody might take it," he said.

He rose again restlessly, and reiterated his first words.

"How do I know? The Indians may be hidden in the house."

He waited again. I drew back behind the half curtain of the bed. He looked about the room, with a vacant glitter in his eyes. It was a breathless moment. There was a pause of some sort. A pause in the action of the opium? a pause in the action of the brain? Who could tell? Everything depended, now, on what he did next.

He laid himself down again on the bed!

A horrible doubt crossed my mind. Was it possible that the sedative action of the opium was making itself felt already? It was not in my experience that it should do this. But what is experience, where opium is concerned? There are probably no two men in existence on whom the drug acts in exactly the same manner. Was some constitutional peculiarity in him, feeling the influence in some new way? Were we to fail on the very brink of success?

No! He got up again abruptly. "How the devil am I to sleep," he said, "with THIS on my mind?"

He looked at the light, burning on the table at the head of his bed. After a moment, he took the candle in his hand.

I blew out the second candle, burning behind the closed curtains. I drew back, with Mr. Bruff and Betteredge, into the farthest corner by the bed. I signed to them to be silent, as if their lives had depended on it.

We waited - seeing and hearing nothing. We waited, hidden from him by the curtains.

The light which he was holding on the other side of us moved suddenly. The next moment he passed us, swift and noiseless, with the candle in his hand.

He opened the bedroom door, and went out.

We followed him along the corridor. We followed him down the stairs. We followed him along the second corridor. He never looked back; he never hesitated.

He opened the sitting-room door, and went in, leaving it open behind him.

The door was hung (like all the other doors in the house) on large old-fashioned hinges. When it was opened, a crevice was opened between the door and the post. I signed to my two companions to look through this, so as to keep them from showing themselves. I placed myself - outside the door also - on the opposite side. A recess in the wall was at my left hand, in which I could instantly hide myself, if he showed any signs of looking back into the corridor.

He advanced to the middle of the room, with the candle still in his hand: he looked about him - but he never looked back.

I saw the door of Miss Verinder's bedroom, standing ajar. She had put out her light. She controlled herself nobly. The dim white outline of her summer dress was all that I could see. Nobody who had not known it beforehand would have suspected that there was a living creature in the room. She kept back, in the dark: not a word, not a movement escaped her.