In late 19th century Mexico, Federales capture Quintero (Fernando Rey), a revolutionary who attempts to rally those opposing the dictatorship of President Díaz. Before going to prison, Quintero gives his lieutenant, Maximiliano O'Leary (Reni Santoni), $600 () with which to continue the cause. Bandit chief Carlos Lobero (Frank Silvera) demands that the money be used for guns and ammunition, but Max instead crosses the border in search of Chris Adams (George Kennedy): a legendary, American gunman whom his cousin had told him about. Max finally finds the laconic Chris, witnessing him free a man from a rigged trial, first by using his wits, then with the famed hair-trigger skill as a gunfighter.