Italy, 1816, during the turbulent years of the Restoration. Fulvio Imbriani, a Lombard aristocrat and member of the secret revolutionary order known as the Sublime Brothers, is arrested by the police. Once released, he is immediately suspected of betrayal by his comrades—especially after the mysterious death of their leader, Filippo. In truth, Filippo took his own life.
Disillusioned and bitter, Fulvio longs to leave the revolution behind and find peace in the care of his family. Yet he cannot bring himself to confess this to the others. Unaware of his change of heart, the Brothers pull him back into one last revolutionary mission.
Eventually, drained and disconnected from the cause, Fulvio betrays them. The Brothers are massacred by angry peasants. Only the young Allonsanfan survives, wounded. In a feverish state, he lies to Fulvio, telling him the uprising was a success and that the peasants have joined the revolution.
Revived by this illusion and the ideals he never fully abandoned, Fulvio puts on the red shirt of the revolutionaries one final time—only to be shot dead by soldiers shortly afterward.