How was the narrator freed? What is the irony of his sudden freedom?

 The cell heats up further and begins to flatten into a narrowing diamond so that the narrator will eventually be forced into the pit. The narrator clings to the heated walls but is ultimately forced to the brink of the pit and screams in despair. As he is about to fall in, however, he hears voices and trumpets as the walls return suddenly to their normal shape. Having just led the French army into Toledo and beaten back the forces of the Inquisition, General Lasalle rushes in and catches the fainting narrator by the arm before he falls into the pit. I suppose the irony is that after using all of his intelligence and resourcefulness to save himself, the narrator is ultimately saved by someone else.   

no