Dario Ferretti, undefeated MMA champion Thunder, refuses to throw a fight for crime boss Cláudio Drummond. His wife Lorena is murdered, his leg injured, forcing him into disguise. His son Caio secretly enters underground fight clubs for his father's surgery. Businesswoman Valentina Ferreira allies with Dario. Dario returns to the ring as Thunder, defeats Hugo, and Drummond is arrested. Caio becomes champion, challenging his father's undefeated record.