four o'clock
The fog seemed to have cleared from the room somewhat , but since in the midnight stillness I could detect the muffled sounds of sirens from the river and the reports of fog signals from the railways , I concluded that the night was not yet wholly clear of the choking mist . In accordance with a pre-arranged scheme we had decided to guard `` the key of India '' -LRB- whatever it might be -RRB- turn and turn about through the night . In a word -- we feared to sleep unguarded . Now my watch informed me that four o'clock approached , at which hour I was to arouse Smith and retire to sleep to my own bedroom . Nothing had disturbed my vigil -- that is , nothing definite . True once , about half an hour earlier , I had thought I heard the dragging and tapping sound from somewhere up above me ; but since the corridor overhead was unfinished and none of the rooms opening upon it yet habitable , I concluded that I had been mistaken . The stairway at the end of our corridor , which communicated with that above , was still blocked with bags of cement and slabs of marble , in fact .