The man was so intent on watching someone, or something, that he did not guard against being himself watched.

This suited Adam, for he could thus make scrutiny at will.
The thick wood, though the trees were mostly of small girth, threw a heavy shadow, so that the steep declension, in front of which grew the tree behind which the African lurked, was almost in darkness.

Adam drew as close as he could, and was amazed to see a patch of light on the ground before him; when he realised what it was, he was determined, more than ever to follow on his quest.

The nigger had a dark lantern in his hand, and was throwing the light down the steep incline.

The glare showed a series of stone steps, which ended in a low-lying heavy iron door fixed against the side of the house.