You know how careless they are.

I went round the hall, and then I went to bed.

But, of course, I wondered about it," said Mrs.Carruthers.
Mr.Flexen looked at her refined, rather delicate face, and he did not wonder how she had repressed her natural curiosity.
"Can you tell me whether the French window in the library, the end one, was open at that time ?" he said.
"I can't," she said in a tone of regret.

"I couldn't very well open the library door.

If the door between the library and the smoking-room was open, I should have been certain to hear something that was not meant for my ears.