Mingled with this explanation were derogatory opinions of some one, delivered with extraordinary bitterness.

From the context it would seem that those remarks were meant to apply to Peter Johnson.

Listening intently, Peter seemed to hear from the first floor a feeble drumming, as of one beating the floor with bound feet.

Then the tumult broke out afresh.
Peter went back to his cell and lit his lamp.

Leaving the door wide open, he coiled the rope neatly and placed it upon his table, laid the hacksaw beside it, undressed himself, blew out the light; and so lay down to pleasant dreams..