Fergus was glad of his departure.

He had been so depressed that he was useless as a companion and, so long as he remained there, he altogether prevented any plan of escape being attempted; for difficult as it might be for one person to get away, it would be next to impossible for two to do so.
For an hour in the day, the prisoners had leave to walk on the wall.

His fellow prisoner had never availed himself of this privilege; but Fergus always took his daily exercise, partly to keep himself in health, partly in hopes that a plan of escape might present itself.

A sentry, however, was always posted on the wall while the prisoners were at exercise; and on the side allotted for their walk, the rock sloped away steeply from the foot of the wall.
The thought of escape, therefore, in broad daylight was out of the question; and Fergus generally watched what was going on in the courtyard.
In time he came to know which was the entrance to the apartments of the governor and his family, where the married officers were quartered, and where the soldiers lodged.

He saw that on the ground floor of the tower he occupied were the quarters of a field officer belonging to the garrison.
One day he saw a number of men employed in clearing out some unused quarters, on one side of the outer courtyard, and judged that an addition was about to be made to the garrison.