Decorated Vietnam hero Frank Vega (Danny Trejo) returns home only to get shunned by society, leaving him without a job and deserted by his high school sweetheart. Forty years later, Frank is forced into a confrontation on a commuter bus to protect an elderly man from a pair of skinheads, turning him into a local hero and an internet sensation known as "Bad Ass". But his good fortune suddenly turns for the worse when his war buddy Klondike is murdered by organized crime, and the police aren't doing anything about it. Now, Frank will enforce his own brand of vigilante justice to bring the killers in.