When Hedwig opened the upper door and closed it behind her, the sound was distinctly audible to his quick ears, and he probably listened and speculated, and finally yielded to his curiosity.
However that may have been, he found Temistocle asleep in the tower basement, saw the key in the lock, guessed whence the noise had come, and turned it.

The movement woke Temistocle, who started to his feet, and recognised the tall figure of the baron just entering the door.
Too much confused for reflection, he called aloud, and the baron disappeared down the stairs.

Temistocle listened at the top, heard distinctly the shutting and locking of the lower door, and a moment afterwards Benoni's voice, swearing in every language at once, came echoing up.
"They have escaped," said Temistocle to himself.

"If I am not mistaken, I had better do the same." With that he locked the upper door, put the key in his pocket, and departed on tiptoe.

Having his hat and his overcoat with him, and his money in his pocket, he determined to leave the baron shut up in the staircase.