The staircase refers to a wrought-iron circular staircase that was originally made by Mary and lead from the Parlor to the second floor artist studios at Lady Sally's Place. After Lady Sally's closed it was installed at Callahan's Place by Mary at the beginning of Callahan's Secret to provide easier access to the roof.
The staircase was destroyed at the end of Callahan's Secret along with the rest of Callahan's Place.