1476, Florence. Giovanni Auditore, an assassin, attempts to thwart a conspiracy against one of Lorenzo de Medicis allies. The ensuing inquiry will take him to Milan where he tries to prevent the worst from happening.

Pursuing Sforza's assassin's, Giovanni arrives in Venice where he intercepts a coded letter from the members of the conspiracy. Decoding this document in order to get to the top of the conspiracy becomes of extreme importance.

Unable to decode the letter, Giovanni decides to deliver it to Rome in order to unmask the ringleaders. But there he discovers that the conspiracy is much more widespread and dangerous than he thought.