Three years after the destruction of the Death Star, the Imperial fleet, led by Darth Vader, dispatches Probe Droids across the galaxy to find Princess Leia's Rebel Alliance, with one probe locating the rebel base on the ice planet Hoth. A wampa captures Luke Skywalker before he can investigate the probe, but he escapes by using the Force to retrieve his lightsaber and wound the beast. Before succumbing to hypothermia, the Force spirit of Luke's deceased mentor, Obi-Wan Kenobi, instructs him to go to the swamp planet Dagobah to train as a Jedi Knight under the Jedi Master Yoda. Han Solo discovers Luke and insulates him against the weather inside his deceased tauntaun mount until they are rescued the next morning.

Alerted to the Rebels' location, the Empire launches a large-scale attack using AT-AT walkers to capture the base, forcing the Rebels to evacuate. Han and Leia escape with C-3PO and Chewbacca aboard the Millennium Falcon, but the ship's hyperdrive malfunctions. They hide in an asteroid field, where Han and Leia grow closer amid the tension. Vader summons several bounty hunters, including Boba Fett, to find the Falcon. Evading the Imperial fleet, Han's group travels to the floating Cloud City on the planet Bespin, which is governed by his old friend Lando Calrissian. Fett tracks them there and Vader forces Lando to surrender the group to the Empire, knowing Luke will come to their aid.

Meanwhile, Luke travels with R2-D2 in his X-wing fighter to Dagobah, where he crash-lands. He meets Yoda, a diminutive creature who reluctantly accepts him as his Jedi apprentice after conferring with Obi-Wan's spirit. Yoda trains Luke to master the light side of the Force and resist negative emotions that will seduce him to the dark side, as they did Vader. Luke struggles to control his anger and impulsiveness and fails to comprehend the nature and power of the Force until he witnesses Yoda use it to telekinetically lift the X-wing from the swamp. Luke has a premonition of Han and Leia in pain and, despite Obi-Wan's and Yoda's protestations, abandons his training to rescue them. Although Obi-Wan believes Luke is their only hope, Yoda asserts that "there is another."

Leia confesses her love for Han before Vader freezes him in carbonite to test whether the process will safely imprison Luke. Han survives and is given to Fett, who intends to collect his bounty from Jabba the Hutt. Lando frees Leia and Chewbacca, but they are too late to stop Fett's escape. The group fights its way back to the Falcon and flees the city. Luke arrives and engages Vader in a lightsaber duel over the city's central air shaft. Vader overwhelms Luke, severing his right hand and separating him from his lightsaber. He urges Luke to embrace the dark side and help him destroy his master, the Emperor, so they may rule the galaxy together. Luke refuses, citing Obi-Wan's claim that Vader killed his father, prompting Vader to reveal that he is Luke's father. Desperate, Luke drops into the air shaft and is ejected beneath the floating city, latching onto an antenna. He reaches out through the Force to Leia, and the Falcon returns to rescue him. TIE fighters pursue the group, which is almost captured by Vader's Star Destroyer until R2-D2 reactivates the Falcon's hyperdrive, allowing them to escape.

Aboard the Rebel fleet, a robotic prosthesis replaces Luke's hand. He, Leia, C-3PO, and R2-D2 observe as Lando and Chewbacca depart on the Falcon to find Han.