He was in the next room.
"Do not put the sword away," she heard him say.

"Leave it here on the table." Of course; what should he do with a sword in his court dress?
But if he had met her father in the corridor, coming to her after the supper, he would have been unarmed.

Her father, on the contrary, being on actual duty, wore the sword of his rank, like any other officer of the guards, and the King wore a rapier as a part of his state dress.
She was astonished at the distinctness with which she heard what was said in the next room.

That was doubtless due to the construction of the vault, as she vaguely guessed.

It was true that Don John spoke very clearly, but she could hear the servants' subdued answers almost as well, when she listened.