He was born in the diocese of Lucca, at Pistoia, and had been ordained a priest by the Bishop of Arezzo.

Some time after his entrance into the priesthood, he had become the pupil of a thaumaturge of Florence, Jean de Fontenelle, and had signed a pact with a demon named Barron.

From that moment onward, this insinuating and persuasive, learned and charming abbe, must have given himself over to the most abominable of sacrileges and the most murderous practices of black magic.
At any rate Gilles came completely under the influence of this man.

The extinguished furnaces were relighted, and that Stone of the Sages, which Prelati had seen, flexible, frail, red and smelling of calcinated marine salt, they sought together furiously, invoking Hell.
Their incantations were all in vain.

Gilles, disconsolate, redoubled them, but they finally produced a dreadful result and Prelati narrowly escaped with his life.
One afternoon Eustache Blanchet, in a gallery of the chateau, perceives the Marshal weeping bitterly.