He had already revolved in his mind every possible mode of escape.

He had tried the strong iron bars of the window, but found that they were so rigidly fixed and embedded in the stonework, that there was no hope of escape in this way; and even could he have got through the window, the weight of his shackles would have crippled him.
He was fastened with two chains, each about two feet six inches long, going from the wrist of the right hand to the left ankle, and from the left hand to the right ankle.

Thus he was unable to stand quite upright, and anything like rapid movement was almost impossible.

The bottom of the window came within four feet of the ground, and it was only by standing on one leg, and lifting the other as high as he could, that he was able to grasp one of the bars to try its strength.
The news he had heard from his fellow prisoner almost maddened him, and he thought far less of his own fate, than of that of the girls, who would be living in their quiet country retreat in ignorance of danger, until suddenly seized by Mocenigo and his band of pirates.
He had, on the first day, tried whether it was possible to draw his hand through the iron band round his wrist, but had concluded it could not be done, for it was riveted so tightly as to press upon the flesh.
Therefore there was no hope of freeing himself in that manner.

The only possible means, then, would be to cut through the rivet or chain, and for this a tool would be required.
Suddenly an idea struck him.