In "Star Wars: Episode III—Revenge of the Sith," Palpatine rescues Darth Vader after Vader's duel with Obi-Wan Kenobi. Obi-Wan defeats Anakin Skywalker on Mustafar, severing his remaining limbs and leaving him badly burned beside the lava river.
Palpatine, who is secretly Darth Sidious, senses that his new apprentice is in danger and travels to Mustafar. He finds Anakin alive but gravely injured, carries him away, and brings him to Coruscant for medical treatment. There, surgeons place Anakin inside the black life-support armor that becomes essential to Darth Vader's survival.
The scene is important because it completes Anakin's transformation from Jedi Knight into Sith Lord. Palpatine also manipulates Vader afterward by telling him that his actions caused Padmé Amidala's death. Viewers sometimes confuse this rescue with Obi-Wan's earlier mission to rescue Chancellor Palpatine from General Grievous, but that occurs near the beginning of the same film. The two rescues involve different characters and happen at opposite ends of the story.