A new, incomplete Death Star hangs over the forest moon of Endor like a malevolent sphere of evil. From a nearby Super Star Destroyer, a shuttle and two TIE fighters emerge and enter the station.
The shuttle is carrying Darth Vader, who in turn carries the news that the Emperor himself will personally oversee the final stages of construction of the Death Star.
Lightyears away, on the planet Tatooine, the two droids C-3P0 and R2-D2 have been given a mission by Luke Skywalker: bring a message to the crimelord Jabba the Hutt. Once they reach Jabba's palace, Artoo delivers the message, in which Luke offers a bargain for Han Solo's life to Jabba and gifts him with the two droids. While the slug-like Jabba declares that there will be no bargain, Threepio and Artoo are taken down to the bowels of the palace to be fitted with restraining bolts and given assignments.
In Jabba's court, meanwhile, a bounty hunter named Boushh brings Chewbacca to the crimelord, who ends up paying him thirty-five thousand credits for the bounty after Boushh threatens him with a thermal detonator. Chewie is taken down to the dungeons.
That night, Boushh sneaks into the court and releases Han from his carbonite prison. When he asks who Boushh is, the bounty hunter removes his helmet, revealing the face of none other that Princess Leia Organa. They are captured before they can escape, however.
Luke arrives the next morning. He tries to use a Jedi mind trick to force Jabba to free his friends, but Jabba lures him to stand on a trapdoor which leads down to the lair of a huge beast called the rancor. Luke fights the monster and succeeds in killing it by trapping under a massive door.
Jabba, understandably miffed at the loss of his pet, sentences Luke, Han, and Chewie to death in the Great Pit of Carkoon. Luke , however, has smuggled his lightsaber into the palace by secreting it in Artoo's storage compartment. Since Artoo accompanies the sail barge which takes Jabba and his courtiers to the Pit, so does the lightsaber. Just as Luke is about to be prodded into the pit, Artoo ejects the lightsaber. Luke catches it, and a pitched battle ensues, in which Leia uses her own chains to choke Jabba to death. Then they use the large gun on the barge to destroy it. Piloting one of the smaller sandspeeders, the Rebels escape.
While Han, Leia, Chewie and Threepio return to the Alliance rendezvous in the Millenium Falcon, Luke and Artoo journey back to Dagobah in his X-wing to complete his Jedi training with Yoda. When they arrive, however, Yoda is close to death. He confirms that Darth Vader is Luke's father, and then gives him the cryptic remark that "There is another Skywalker." before dying. Luke questions Obi-Wan Kenobi's specter, who reveals that Luke has a twin sister. Luke then realizes that his sister is Leia.
On the Death Star, the Emperor, a stooped, wasted man, arrives. Though Darth Vader wants to search for Luke, Palpatine assures him that Luke will seek him out. Only together can they turn Luke to the dark side of the Force.
At the Alliance rendezvous, the Rebels hold a hurried briefing to outline their plan of attack on the second Death Star. Lando Calrissian and Wedge Antilles are to lead the fighter attack, while the Calamarian Admiral Ackbar is in charge of the fleet. Han, along with Leia, Luke, and Chewie, must use a stolen Imperial code and shuttle to penetrate the shield, land on Endor, and destroy the shield generator, opening the Death Star to attack.
They manage to land on the moon, but there is a tense moment as Darth Vader seems to sense something. Finally, though, he instructs Imperial Admiral Piett to leave the shuttle to him. The strike team lands on Endor, but are almost immediately beset with trouble. Han and Chewie try to ambush a stormtrooper patrol, but they fight back and two of them get away on speeder bikes. Luke and Leia, knowing that they can't have their presence revealed, pursue on another speeder. After a long chase, Luke uses his lightsaber to cause a stormtrooper to crash, and Leia leaps from her speeder, distracting the other and causing him to crash as well.
Leia, knocked unconscious, wakes to encounter a small, bear-like creature who saves her from yet another stormtrooper by distracting it while she hits it with a tree limb. Then the little alien leads her away into the forest.
Luke returns to the strike team, and he, Han, Chewie, and the droids search for Leia while the rest of the strike team goes on ahead.
After a fruitless search in which they only find wreckage, Chewie finds the carcass of a dead animal. He tries to grab it, but the whole party is swept up into a trap. Artoo uses a cutting tool to free them, but not before they are surrounded by several Ewoks, the same sort of creature that Leia encountered.
They take Han, Luke, Chewie, and Artoo prisoner, but Threepio they rever as a god. They are taken to the Ewoks' village, where Luke uses the Force to levitate Threepio, thoroughly scaring the Ewoks, who free the rest of them. They are reunited with Leia, who has also ended up at the village. Threepio tells their story, and the Ewoks decide to help the Rebels fight the Empire.
Luke cannot find much joy in it, however, and goes off to be alone. Leia follows him, and he tells her that not only is Vader his father, but Leia is his sister. Then he leaves to confront their father.
Vader's shuttle lands on Endor, where he meets Luke, who has turned himself in to the Imperials. Luke tries to turn Vader back to the light side, but Vader stays with his master, the Emperor, and Luke is taken up to the Death Star.
While the Rebel Alliance fleet sets out for Endor, the strike team penetrates the control bunker with the help of the Ewoks. However, they are surprised by a squad of stormtroopers who enter behind them. They are taken out into the clearing before the bunker, where an entire legion of Imperials is waiting for them.
Three simultaneous battles take place. The first is the mental battle between Luke and the Emperor. Luke holds out against the dark side for a time, but soon snatches his lightsaber and strikes at the Emperor. Darth Vader parries the blow, and they begin a duel. Luke doesn't want to fight his father, and hides. Vader draws him out by threatening to turn Leia to the dark side. At this point, Luke snaps and attacks Vader viciously, severing his hand. Though he is close to the dark side, Luke is able to pull away. The Emperor loses patience with him and starts pelting him with Force lightning.
Above the forest moon, the Rebel fleet is having problems. Not only is the shield still up, but the Death Star is operational, and ships are being lost to the superlaser. Lando urges Admiral Ackbar, the Mon Calamari in command, to engage the Imperial fleet, hoping that Han will be able to get the shield down.
On Endor, an army of Ewoks ambushes the stormtroopers, and a pitched battle occurs. While Leia and Han hide in the bunker entrance, trying to get the door open, Chewie and two Ewoks capture one of the All-Terrain Scout Transports (AT-ST's), which have been wreaking havoc among the Ewok warriors. Leia gets shot, but she still manages to surprise two stormtroopers attempting to capture them, and the rest flee into the woods. They gain entrance to the bunker by posing as Imperials.
After the shield generator is destroyed, Lando, Wedge Antilles, and several other fighters enter the Death Star's superstructure, while the rest of the fleet concentrates all fire on the Super Star Destroyer.
Darth Vader cannot bear to watch his son killed by the Emperor. Anakin Skywalker reemerges, tearing himself away from the dark side. He grabs the Emperor and throws him into the hollow shaft that leads down deep into the Death Star. Anakin is severely electrocuted, and is near death.
Wedge and Lando have reached the power generator. Wedge targets the power regulator, while Lando fires on the main generator. Their shots cripple the generator, and fire chases them out of the Death Star.
Han, even though he loves Leia, tells her that he won't get in the way when Luke returns. He is quite overjoyed when Leia informs him that Luke is really her brother.
Luke escapes on a shuttle with Anakin's body just as the shuttle bay erupts in flames. He lands the shuttle on Endor, where the Ewoks have already begun to celebrate. After cremating Anakin on a funeral pyre, Luke is reunited with his friends. Everyone joins in, and hugs are exchanged all around. Hovering at the edge of the celebration are the spirits of three Jedi: Obi-Wan, Yoda, and Anakin. Luke, overjoyed at seeing his father one with the Force, allows Leia to pull him back into the aura of joy that surrounds the Rebels. Good has triumphed over evil.