The Corner House by Fred M. White

There was the sound of a faint scratching as if a mouse was working somewhere. The warder in the courtyard pronounced it to be a mouse, and pushed on. Then a figure, almost invisible in the gloom, crept along the top of the wall and dropped feet foremost into the street. It was nothing but luck that stood Rene Lalage in such good stead all along. A crumbling bit of plaster, some repairs going on in the gallery overhead, a ladder, and a couple of gimlets left about by one of the carpenters engaged on the job.

Well, he was free. He did not hesitate for a moment. He darted swiftly down the road with the air of a man who knows exactly what he is doing and where he wants to go. The man had not been convicted yet, therefore he had the advantage of wearing his own clothes.