I know his knock.

Will you come and see him ?" The wife was trembling, she was very pale, her eyes were rather staring, but she fought to control herself.

It was evident that Kitty expected her to do so.

It was also quite certain that Kitty meant to settle things now, in so far as it could be done.
"He knows as much as you do ?" asked Mrs.Crozier.
"No, the Young Doctor hasn't read the letter and I haven't told him what's in it; but he knows that I read it, and what he doesn't know he guesses.

He is Mr.Crozier's honest, clever friend.