A mysterious gunman (Eastwood) has just arrived in San Miguel, a grim, dusty border town where two rival bands of smugglers are terrorizing the impoverished citizens. A master of the 'quick draw', the stranger soon receives offers of employment from each gang. But his loyalty cannot be bought; he accepts both jobs ... and sets in motion a plan to destroy both groups of criminals, pitting one against the other in a series of brilliantly orchestrated setups, showdowns, and deadly confrontations.