He agreed with the Florentines to receive from them a yearly tribute of two hundred thousand florins, and he send his son Carlo to Florence with four thousand horsemen.
Shortly after this the Florentines were relieved in some degree of the pressure of Castruccio's army, owing to his being compelled to leave his positions before Florence and march on Pisa, in order to suppress a conspiracy that had been raised against him by Benedetto Lanfranchi, one of the first men in Pisa, who could not endure that his fatherland should be under the dominion of the Lucchese.

He had formed this conspiracy, intending to seize the citadel, kill the partisans of Castruccio, and drive out the garrison.

As, however, in a conspiracy paucity of numbers is essential to secrecy, so for its execution a few are not sufficient, and in seeking more adherents to his conspiracy Lanfranchi encountered a person who revealed the design to Castruccio.
This betrayal cannot be passed by without severe reproach to Bonifacio Cerchi and Giovanni Guidi, two Florentine exiles who were suffering their banishment in Pisa.

Thereupon Castruccio seized Benedetto and put him to death, and beheaded many other noble citizens, and drove their families into exile.

It now appeared to Castruccio that both Pisa and Pistoia were thoroughly disaffected; he employed much thought and energy upon securing his position there, and this gave the Florentines their opportunity to reorganize their army, and to await the coming of Carlo, the son of the King of Naples.