Despite their victory over the Galactic Empire with the destruction of the Death Star, the Empire's forces have driven the Rebel Alliance into hiding, forcing the fleet to establish a hidden base on the remote ice planet Hoth. Darth Vader, having become obsessed with finding Luke Skywalker, has multiple probe droids dispatched throughout the galaxy, one of which lands on Hoth. While patrolling near the base, Luke is attacked and knocked unconscious by a Wampa. Back at the base, Han Solo announces his intentions to leave the Rebellion to pay off a debt to Jabba the Hutt (much to Princess Leia's displeasure). When Luke doesn't return that evening, Han braves the deadly Hoth night to find his lost friend. Escaping from the creature's lair, Luke nearly succumbs to the cold and has a vision of his late mentor, Obi-Wan Kenobi, who instructs him to go to the planet Dagobah to train under Jedi Master Yoda.
Han finds Luke and provides shelter before they are rescued the following morning. Meanwhile, the Imperial probe droid locates the Rebel base on Hoth, and Vader orders an attack while the Rebels prepare to evacuate and disperse. The Imperial forces eventually overpower the Rebels and capture the base. Han and Leia escape on the Millennium Falcon with C-3PO and Chewbacca, but are unable to enter hyperspace due to technical difficulties. They evade pursuit in an asteroid field where Han and Leia begin to grow closer to each other. Vader turns to several notorious bounty hunters, including Boba Fett, to assist in locating the Falcon. Meanwhile, Luke escapes from Hoth with R2-D2 and crash lands on Dagobah where he meets Yoda. While undergoing intensive training, Luke has a premonition of Han and Leia in pain and, against Yoda's wishes, leaves to save his friends, promising to return to complete his training.
After losing the Imperial forces, and unaware that they have been tracked by Fett, Han's party sets a course for Cloud City, a floating gas mining colony in the skies of the planet Bespin, which is run by Han's old friend, Lando Calrissian. Shortly after they arrive at Cloud City, Lando turns them over to Vader to be used as bait in a trap for Luke. Lando insists to Han and Leia that he was forced to betray them to prevent the occupation of his city by the Empire. Vader straps Han to a torture machine and, while not permanently harmed, he is tormented to the point that he can barely stand. Luke sees these premonitions of his friends in pain and abandons his training to help them.
Vader intends to hold Luke in suspended animation via carbon freezing, and selects Han as a test subject for the process. Before Han is frozen in the carbonite freezing chamber, Leia professes her love for him. Han acknowledges that "he knows". Vader gives Han's hibernating form to Fett, who plans to present this "prize" to Jabba the Hutt. Lando repents and helps Leia and the others escape, insisting that there is still a chance to save Han. Unfortunately, Fett makes off with his quarry just seconds before they get a chance to confront him, forcing them to make an escape on the Millennium Falcon.
Meanwhile, Luke arrives at Cloud City and falls right into Vader's trap. Within the carbon-freezing facilities, Luke and Vader engage in a vicious lightsaber duel, which leads them over the city's central air shaft. Gaining an advantage, Vader cuts off Luke's dueling hand along with his lightsaber. With Luke cornered and defenseless, Vader tempts Luke with the offer to rule the galaxy alongside him, making the revelation that he is in fact Luke's father. Horrified, Luke casts himself into the air shaft, plummeting until he reaches a tube system that spills him out onto an antenna attached to the underbelly of the city. He makes a desperate call to Leia, who senses Luke's distress aboard the Millennium Falcon and gets him to safety. Its hyperdrive finally functional (thanks to timely repairs by R2-D2), the Falcon escapes. Aboard a Rebel medical frigate, a medical droid fits Luke with an artificial hand. Lando and Chewbacca set out on the Falcon to locate Han.