Sentence:  When Timothy and Julia hurried up the <WSD>staircase</WSD> to the bedroom floor, where a considerable commotion was taking place, Tim took Barry Leach with him. He had him gripped firmly by the arm, since he felt it was not safe to let him loose, and he had no immediate idea what to do with him. 
Meaning of the word marked with <WSD> tags:  A connected set of flights of stairs; a stairwell.