Ezio's memories begin during the Renaissance in the 15th century, where his family is ensnared in a political plot, and his father and brothers are hanged. Ezio, following his father's last advice, finds his father's Assassin tools, and flees the city with his mother and sister to the safety of his uncle Mario's villa in the countryside. Mario assists Ezio in discovering the people behind the conspiracy, the search leading Ezio from Florence, to San Gimignano, Forlì, Venice and eventually to Rome. As he identifies and assassinates more and more political figures, Ezio also gains several allies, including Niccolò Machiavelli and Leonardo da Vinci, the latter of whom helps Ezio improve his equipment using schematics found in Altaïr's Codex pages. Ezio eventually identifies the mastermind of the plot: the Spaniard Rodrigo Borgia, who ultimately sought to bring down the Medici family in Florence with the help of the Pazzi family and theDoge of Venice. Ezio finds Borgia in possession of the Apple-- the same Piece of Eden that Altaïr had recovered centuries ago-- and learns that Borgia believes himself to be "The Prophet" that will lead the Templars to a fabled "Vault". Ezio is able to confront Borgia with the help of his allies and recover the Apple, and Borgia flees before he can be killed. Ezio's allies reveal they are all Assassins, and see Ezio as their Prophet, allowing him to join their ranks.
Source from Wikipeida