Summary
In the American Southwest during the Civil War, a mercenary known as "Angel Eyes" interrogates a former Confederate soldier to learn the alias of a man who stole a stash of Confederate gold. The soldier, Stevens, reveals the man's alias, Bill Carson, and attempts to bribe Angel Eyes to kill his employer before drawing on him. Angel Eyes kills him and, returning to his employer, kills him as well.
Mexican bandit Tuco Ramírez, fleeing from bounty hunters, is captured by an unnamed drifter he nicknames "Blondie" who delivers him to a sheriff and collects the bounty. As Tuco is about to be hanged, Blondie severs the noose with a rifle bullet and the two escape to split the bounty. They repeat the process in another town but Blondie grows weary of Tuco's complaints, keeps the money, and strands Tuco in the desert.
Bent on revenge, Tuco reassembles his gang and tracks down Blondie. Although his gang dies in a failed ambush, Tuco captures Blondie in his hotel room and prepares to hang him. An artillery round destroys the room, allowing Blondie to escape. After a lengthy pursuit, Tuco recaptures Blondie and force-marches him through the desert until he collapses from dehydration. A runaway ambulance arrives with several dead Confederate soldiers and a barely alive Bill Carson. Near death, Carson begs Tuco for help, offering $200,000 in gold buried in Sad Hill Cemetery. When Tuco returns with water, Carson has died, having revealed the exact location of the gold to Blondie.
The two reluctantly agree to work together, unwilling to disclose their knowledge of the gold's location. They pose as Confederate soldiers at a mission while Blondie recovers and Tuco reunites with his brother, a priest, who rejects Tuco. They leave the mission and are taken prisoner by Union cavalry. Tuco gives the name Bill Carson, alerting Angel Eyes, who has infiltrated the prison camp as a Union sergeant. Tuco is tortured into revealing the cemetery's name and sent away to be hanged. Knowing torture won't work on Blondie, Angel Eyes joins forces with him. Tuco escapes from custody and tracks Angel Eyes' gang to a ghost town.
Distrusting of Angel Eyes, Blondie finds Tuco and kills the gang members, but Angel Eyes escapes. Tuco and Blondie witness a battle over a strategic bridge they need to cross, and blow it up to disperse the armies and clear their path. As they wire the bridge with explosives, Tuco suggests they exchange their secrets in case either is killed. Tuco reveals the cemetery's name, and Blondie says "Arch Stanton" is the name on the grave.
After the bridge is demolished, Tuco rushes towards Sad Hill to claim the gold for himself. Blondie catches up with him as he digs up the grave, and Angel Eyes arrives soon after. When no gold is found in the grave, Blondie admits lying about the name. He then places a stone in the middle of the cemetery's pavement, on which he says the true name is written. The three men face each other in a Mexican standoff. Angel Eyes draws first, but Blondie shoots him before he can fire. Tuco finds that his gun is empty and, as Blondie walks confidently toward him, realises that Blondie unloaded it earlier.
Blondie reveals that the gold is in the grave next to Stanton's marked "Unknown". After Tuco digs up several large bags of gold, Blondie orders him at gunpoint into a hangman's noose. With hands bound, Tuco stands atop a rickety grave marker while Blondie takes half the gold and rides away. As Tuco screams for mercy, Blondie severs the rope with a rifle shot, dropping Tuco face-first onto the remaining gold. Tuco furiously curses Blondie, who smiles before riding over the nearby hills.
Source: Wikipedia (CC BY-SA 3.0)