During a space battle over the planet Coruscant between the Galactic Republic and the Separatists, Jedi Knights Obi-Wan Kenobi and Anakin Skywalker lead a mission to rescue the kidnapped Supreme Chancellor Palpatine from Separatist commander General Grievous. After infiltrating Grievous' flagship, the Jedi battle the Sith Lord Count Dooku in a lightsaber fight, but Obi-Wan is injured in the process. Anakin eventually subdues Dooku and kills him on Palpatine's urging. Grievous flees the battle-torn cruiser, which the Jedi crash-land on Coruscant. There, Anakin reunites with his wife, Padmé Amidala, who reveals she is pregnant. Initially excited, Anakin begins to have prophetic visions of Padmé dying in childbirth.
Palpatine appoints Anakin to join the Jedi Council as his representative, but the Council declines Anakin the rank of Jedi Master and orders him to spy on Palpatine, which diminishes Anakin's faith in the Jedi. Palpatine entices Anakin with knowledge of the dark side of the Force, including the power to "cheat death", and reveals himself as the Sith Lord Darth Sidious. Anakin reports his treachery to Mace Windu, who attacks and subdues Palpatine with his lightsaber. Fearing that he will lose Padmé, Anakin intervenes on Palpatine's behalf, allowing him to kill Windu. Anakin pledges himself to Palpatine, who dubs him Darth Vader.
Palpatine issues an order for the clone troopers to kill their Jedi commanders and dispatches Vader and a legion of clones to kill everyone in the Jedi Temple; however, Obi-Wan (having killed Grievous on Utapau), Senator Bail Organa and Yoda survive. Vader then kills the remaining Separatist leaders hiding on the volcanic planet Mustafar, while Palpatine addresses the Senate and transforms the Republic into the Galactic Empire, declaring himself Emperor. On Coruscant, Obi-Wan and Yoda return to the Jedi Temple and discover Anakin's treachery.
Obi-Wan tells Padmé about Anakin's turn to the dark side. Traveling to Mustafar with Obi-Wan as a stowaway, Padmé asks Vader to come back with her, but Vader refuses. Vader discovers Obi-Wan and accuses Padmé of betrayal, using the Force to choke her into unconsciousness. Obi-Wan engages and eventually defeats Vader, takes his lightsaber and leaves him for dead among the planet's lava flows. Back on Coruscant, Yoda fights Palpatine in the Senate Chamber; their duel reaches a stalemate and Bail helps Yoda escape. Palpatine senses that Vader is in danger and he travels to Mustafar.
Regrouping with Yoda, Obi-Wan brings Padmé to the asteroid Polis Massa, where she gives birth to twins Luke and Leia before dying. A funeral is held for Padmé on Naboo. On Mustafar, Palpatine finds Vader badly burnt and mutilated, but still alive. After returning to Coruscant, he rebuilds Vader's ruined body with the black armored suit. Palpatine then tells Vader that Padmé was killed in Vader's anger, breaking what remains of his apprentice's spirit. As Palpatine and Vader watch the construction of the Death Star, Obi-Wan and Yoda plan to hide the twins from the Sith. Yoda exiles himself to the planet Dagobah. Bail adopts Leia and takes her to Alderaan, while Obi-Wan delivers Luke to his stepfamily Owen and Beru Lars on Tatooine, where Obi-Wan intends to watch over Luke until the time is right to challenge the Empire.
- Diesel 10, Splatter and Dodge, Trixie, and Queen Chrysalis guest star in this film.
- The storyline continues in Thomas and Twilight Sparkle's Adventures of Star Wars Episode IV: A New Hope.