And suddenly there was a new danger. The phantom footsteps ceased, and a voice rang out. "Come out at once!" the voice shouted. "Don't imagine that I cannot see you! Come out!" and the voice was the voice of Mr. Port!
Penny was much too frightened to come out. If he wanted her, he would have to drag her out - why, she couldn't even stand on her legs, they were trembling so much! And just as she was making plans to resist to the death, there was a crash, as if the whole school was tumbling down and taking a thousand buckets with it. When the echoes had died down she could hear Mr. Port muttering furiously; then came another crash and a light was switched on.
This is the end, Penny thought, and shut her eyes tight.
From THREEPENNY BIT, Chapter 14, The Clue. Mr. Port, a schoolmaster at Friars and known to the boys as Old Starboard, doesn't appear to be a mild-mannered teacher anymore.