Although repeatedly foiled in his assiduous attempts to break prison, the indomitable Trenck never abated his unshaken desire to compass freedom. At length opportunity offered for a larger and more dangerous project: the seizure of the Star Fort and the capture of Magdeburg. At that time the war was in full progress and the garrison of the fortress consisted of only nine hundred discontented men of the militia. Trenck had already won over two majors and two lieutenants to his interest. The guard of the Star Fort was limited to one hundred and fifteen men. The town gate immediately opposite was held by no more than twelve men under a sergeant; just within it was a barrack filled with seven thousand Croat prisoners of war, several of whose officers were willing to join in an uprising. It was arranged that a whole company of Prussians should turn out at a moment’s notice with muskets loaded and bayonets fixed, to head the attack as soon as Trenck had overpowered the two sentinels who stood over him, secured them and locked them into his cell. It was an ambitious plan and was well worth the attempt. Magdeburg was the great national storehouse, holding all the sinews of war, treasure and munitions, and Trenck in possession, backed with sixteen thousand Croats, might have dictated his own terms. The plot failed through the treachery of an agent despatched to Vienna with a letter, seeking cooperation; it was given into the wrong hands and was sent back to Magdeburg, where the governor, then the landgrave of Hesse-Cassel, read it and took prompt precautions to secure the fortress. An investigation was ordered, and Trenck was formally arraigned as a traitor to his country, but he sturdily denied the authorship of the incriminating letter, and the charge was not brought home to him. The landgrave was more merciful than former governors and showed great kindness to Trenck, relieved him of his intolerable iron collar, sent his own private physician to attend him in his illness and revoked the cruel order that prescribed his incessant awakening during the night.