As soon as it was dark they began the work, relieving each other in turns. The oil prevented much sound being made, but to deaden it still further they wrapped a handkerchief over the file. The bars had been but a short time in position and the iron was new and strong. It was consequently some hours before they completed their work. When they had done, the grating was left in the position it before occupied, the cuts being concealed from any but close observation by kneading up small pieces of bread and pressing them into them, and then rubbing the edges with iron filings.

"That will do for tonight," Malcolm said. "No one is likely to pay us a visit; but if they did, they would not notice the bars unless they went up and shook them. Tomorrow morning we can put a finishing touch to the work."

As soon as it was daylight they were upon their feet.

"It does very well as it is," Malcolm said, examining the grating. "It is good enough to pass, and we need not trouble further about it. Now collect every grain of those iron filings. No, don't do that on any account," he broke in, as Ronald was preparing to blow some of it from the lower stonework through the opening. "Were you to do that, it would be quite possible that one of the prisoners walking in the yard might see it, and would as likely as not report the circumstance to one of the warders in order to curry favour and perhaps obtain a remission of his sentence. Scrape it inside and pour every atom down the crevices in the floor. That done, we are safe unless anyone touches the grating."