Auditore execution

 

"I'll kill you for what you've done!"

―Ezio to Uberto Alberti after watching his family's execution in 1476.

Ezio uncovering his father's equipment

After finishing the errand for his mother, Ezio returned to Giovanni, who requested that he deliver two letters to contacts of his in the city, before retrieving a third letter from a pigeon coop not far from the house.
Ezio agreed, and after two odd encounters with the people he'd delivered the letters to, Ezio retrieved the note from the pigeon coop only to witness guards running across Florence.
Ezio returned home to find his home ransacked, his father and brothers missing, and his mother and sister hiding. Learning that city guards had been ordered to arrest Giovanni and all of his sons, Ezio made his way to the Palazzo della Signoria, where his father and brothers were being held.
Climbing the building and speaking to his father through his cell window, Ezio was instructed to find a chest hidden in his office, take everything out of it, and deliver a sealed letter to Uberto Alberti, Gonfaloniere of Florence and a close friend of the Auditore family. Doing so, Ezio found his father's Assassin robes, a broken Hidden Blade, and a letter containing details of a plot against the city of Florence and the Auditore family.
Ezio brought the incriminating documents to Uberto, and was assured that his family would be released the following day, when the information was presented as evidence of their innocence.Ezio then traveled to the home of Cristina Vespucci, where he spent the night once again.

Guards restraining Ezio at the execution

The next day, Ezio returned to the Piazza della Signoria to find Uberto presiding over the execution of his family.
Giovanni declared their innocence, citing the information given to Uberto as evidence, but the Gonfaloniere denied any knowledge of such information. Ezio shouted that Uberto was lying, but his efforts to prevent the execution were ultimately in vain.
Ezio could only watch helplessly from the crowd as his father and brothers were hanged. When he attempted to charge the gallows to avenge his kin, Uberto ordered the city guards to kill him.
At the urging of one of Giovanni's friends, a thief, Ezio fled the Piazza della Signoria and sought shelter in a brothel run by the sister of the Auditore housemaid, a courtesan named Paola.

Exacting revenge

"The Auditore are not dead! I'm still here! Me! Ezio! Ezio Auditore!"

―Ezio, upon killing Uberto.

Paola, who – unbeknownst to Ezio – was an Assassin herself, agreed to assist Ezio in his quest for vengeance, teaching him how to survive in the city as an outlaw through pickpocketing and blending in crowds. She further directed Ezio to Leonardo da Vinci to repair Giovanni's Hidden Blade, though she did not notice that Ezio was being watched.
After Leonardo repaired the blade, a guard banged on the door and ordered Leonardo outside before trying to beat Ezio's location from him. Ezio realized something was wrong and crept up behind the guard, assassinating him.

Ezio stabbing Uberto Alberti

After Leonardo had thanked him, Ezio sought out and assassinated Uberto in the courtyard of the Basilica di Santa Croce, during Andrea del Verrocchio's latest exhibit.
Once he had made his way into the courtyard, Ezio attacked Uberto in a frenzied rage, stabbing him multiple times in the chest, before proudly proclaiming the survival of the Auditore family, through him.^[1]
After killing Uberto, Ezio took the documents that the Gonfaloniere had concealed from him and his father, as well as a letter from Uberto meant for his wife and son. Ezio decided that he would see to it that she received the letter, not wanting to sink to Uberto's level.