The house was holding its breath.
He had to wait for a breathless, agonising interval before he heard the next sound, very faint and stifled breathing coming up to him out of the darkness in little uncertain gusts.

He heard the breathings pause, then recommence again in quicker and louder succession.

Henry, stirred simply, perhaps, by the terror of his anticipation, moved back into the darker shadows in the nook of the cabinet, and stayed there with his shirt pressed against his little trembling knees.
Then followed, after a long time, a half yellow circle of light that touched the top steps of the stairs and a square of the wall; behind the light was the stealthy figure of Mrs.Carter.She stood there for a moment, one hand with a candle raised, the other pressed against her breast; from one finger of this hand a bunch of heavy keys dangled.

She stood there, with her wide, staring eyes, like glass in the candle-light, staring about her, her red cheeks rising and falling with her agitation, her body seeming enormous, her shadow on the wall huge in the flickering light.

At the sight of his enemy Henry's terror was so frantic that his hands beat with little spasmodic movements against the wall.
He did not _see_ Mrs.Carter at all, but he saw rather the movement through the air and darkness of the house of something that would bring down upon him the full naked force of the Terror that he had all his life anticipated.