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.”