As a youngster residing in Lawless, Angelo Lagusa observed a tragic event: the Vanetti mafia clan ruthlessly killed his parents and younger sibling. Devastated and bereaved, he renounces his name and hometown and assumes the alias Avilio Bruno. Seven years on, Avilio receives an enigmatic letter prompting his return to Lawless, which presents him with the opportunity for revenge. He encounters Nero, the don's son, and endeavors to befriend him with the skills he has refined over the years. 91 Days, situated during the Prohibition era, narrates Avilio's somber journey of vengeance as he methodically eliminates each of the perpetrators involved in his family's slaughter.