To reunite with this dying brother in Los Angeles, the French Foreign Legion officer, Lyon Gaultier, abandons his unit. Penniless, yet determined to make those who harmed his brother pay, Lyon takes part in an illegal street fight and catches the eye of Cynthia Caldera, an unscrupulous organizer of underground fights. However, as Lyon becomes Lionheart, the unpaid medical bills of his sister-in-law, Hélène, start to pile up. Now, the odds are against Lyon, who desperately wants to help his brother's family. Can Lionheart defeat brutal Attila, the undisputed champion of Cynthia's underground fighting matches?