This was once the front entrance of the house, but George Holt made the new front entrance used today. We don’t know why he made this change. This left the staircase at the wrong end of the hall, a long way from the front door.
So Holt built a wall across part of the hall and rebuilt the bottom part of the staircase against it, at a right angle to where it had been before. On the other side of the new wall he added a fireplace.