The bolts were beginning to be withdrawn.

He lifted the lamp, flew across his prison, found the ring, and took a pull at it with desperate strength.

Part of what appeared to be the solid wall drew out, disclosing an aperture through which he could just squeeze sideways.

Quick as thought he was through, forgetting the lamp in his haste.

The portion of the wall slid noiselessly back, just as the prison door was thrown open, and the dwarfs voice was heard, socially inviting him, like Mrs.Bond's ducks, to come and be killed.
Some people talk of darkness so palpable that it may be felt, and if ever any one was qualified to tell from experience what it felt like, Sir Norman was in that precise condition at that precise period.
He groped his way through the blind blackness along what seemed an interminable distance, and stumbled, at last, over the broken stairs at the end.