A Dark Revenge

The USS Enterprise limps back to Earth heavily damaged after a battle with Khan Noonien Singh (see Star Trek II: The Wrath of Khan). Many were lost in the costly fight, including Admiral James T. Kirk's Vulcan friend, Spock; Spock's casket was shot into orbit around the newly-formed Genesis Planet, created by a torpedo designed to create life from lifelessness. On docking, the Enterprise' crew learns that the ship is due to be decommissioned. Dr. Leonard McCoy is confined by security after he begins to exhibit strange behavior. David and Lieutenant Saavik return to Genesis aboard the research vessel USS Grissom; discovering an unidentified lifeform, Marcus and Saavik beam down to the planet and discover that Spock has been resurrected by the Genesis Device's effects, although his mind is no longer present and he operates on a purely child-like level. Marcus, pressed by Saavik, admits that he used unstable "Proto-matter" in building the Genesis device to solve "certain problems". Without it, he claims that the Genesis Project could have been delayed by years or would have never been completed at all. The unstable matter puts the planet in a state of accelerated evolution that will conclude with its premature destruction within a few hours. 
Unknown to them, a Klingon commander named Kruge has intercepted information about Genesis and becomes interested in it (for much of the same reasons as Khan: as a weapon). He travels to the Genesis Planet to learn its secrets after stealing additional information related to it. 
Spock's father, Sarek travels to Earth and confronts Kirk about abandoning Spock's body on the Genesis planet. Sarek discovers, with Kirk's help, that McCoy possesses Spock's "katra" (soul), which explains his strange behavior. Both his katra and body are needed to properly lay him to rest on his homeworld Vulcan; without swift intervention, Spock's consciousness will overwhelm McCoy, and he will also die. Disobeying direct orders prohibiting anyone from visiting the Genesis Planet, Kirk reunites with his bridge officers and goes through a series of highly unorthodox events such as Uhura charming the watch officer (locking him in a closet), Kirk and Sulu springing McCoy from the Starfleet jail, and Scotty overriding the Starbase security system to open the Starbase doors so the Enterprise can escape, and secondly disabling the pursuing USS Excelsior's "transwarp drive", by removing several circuits. 
Kruge arrives at Genesis first, accidentally destroying the Grissom with all hands (save for the landing party). He then summarily executes his weapons officer responsible for the Grissom's destruction as Kruge wanted prisoners. His crew locates and captures the scientists on the planet: David, Saavik, and a now-teenaged Spock. Kirk and the skeleton crew of the Enterprise arrive, unaware that the Klingon ship and its crew are cloaked nearby. Unable to hail the Grissom, the Enterprise crew suspects the presence of a Bird of Prey and are able to strike first, hitting the Klingon ship as it de-cloaks. The Klingon ship returns fire and cripples the automation system controlling the Enterprise. Kruge demands that they surrender, and orders the troops that he had sent to the surface of the Genesis Planet to kill one of the prisoners as a show of strength. David defends Saavik, who was to be the intended victim. David briefly tussles with the Klingon, but is no match with him physically and dies as a result. Kirk is devastated to hear his son has been killed. 
Rather than surrender, Kirk orders McCoy and Sulu to the transporter room. Kirk, Scott and Chekov order the ship to self-destruct, and they leave the Enterprise for the last time. The computer countdown confuses the majority of Kruge's crew who had just beamed over to complete the ship's capture and are all killed as the ship self-destructs. The crew of the Enterprise watch from the planet's surface as their home for the last twenty years burns up in the atmosphere. They find Saavik and Spock and free them from their captors. Kirk finds a communcator and tempts Kruge, who is mourning his crew, in an attempt to get him to beam them all up before the planet destroys itself. Moments later, Kruge beams to the planet and has everyone but Kirk and Spock beamed aboard his Bird of Prey. Still demanding the technology of the Genesis project, Kruge engages Kirk in hand-to-hand combat on the disintegrating planet. Kirk tries in vain to get Kruge to cooperate so they can both escape the planet, but Kruge would prefer a fight to the death. Kirk defeats Kruge who subsequently falls into a volcanic rift. Kirk quickly grabs Spock and imitates Kruge's voice shouting the order to beam them both aboard Kruge's ship. The Enterprise crew are able to easily capture the Klingon vessel and the one crewman left on board. 
The crew travel to Vulcan, where Spock's katra is reunited with his body in a dangerous procedure called "Fal-tor-pan". Dr. McCoy agrees to the ritual, knowing the extreme risk for both him and Spock. The ritual is successful and Spock is resurrected alive and well, though his memories are still extremely fragmented. The final scene, a brief discussion between Kirk and Spock, ends with Spock slowly remembering the man before him: "Jim. Your name is Jim." 
The Galactic Republic is on the verge of collapse as a result of the Clone Wars, which have been waged between the Republic and the Separatists for three years. In a surprise move, General Grievous, commander of the Separatist Droid Army, kidnaps Supreme Chancellor Palpatine and attempts to escape. Jedi Knights Obi-Wan Kenobi and Anakin Skywalker lead a mission to rescue the Chancellor, who is being held captive on Grievous' flagship. There they confront Count Dooku, who is killed by Anakin in a lightsaber duel. The Jedi free the Chancellor and attempt to escape the battle-torn flagship, but Grievous traps them inside and escapes. Fortunately, the Jedi are able to manage an otherwise soft crash landing on Coruscant. Shortly after returning, Anakin reunites with his wife, Padmé Amidala, who reveals that she is pregnant. Anakin is overjoyed with this news until he begins having recurring nightmares of Padmé dying in childbirth, similar to the visions he had of his mother before she died. Anakin resolves to prevent these visions from coming true.
Meanwhile, the Jedi Council has begun to suspect Palpatine of being corrupt and orders Anakin to spy on him, an order Anakin resents since he has grown rather close to Palpatine. Under Palpatine's influence, Anakin begins to grow distrustful of his fellow Jedi, and is intrigued when Palpatine mentions an ability to prevent death. Obi-Wan is sent to the planet Utapau where he engages and kills General Grievous. Back on Coruscant, Palpatine reveals himself to Anakin as the Sith Lord Darth Sidious, who has been controlling both sides of the war. Anakin exposes Palpatine to Jedi Master Mace Windu, who engages and subdues Sidious in a lightsaber duel. Believing that Sidious is his only hope to save Padmé, Anakin intervenes and disarms Windu before he can execute Sidious, allowing the Sith Lord to kill Windu. Anakin submits to the dark side of the Force and becomes Sidious' new apprentice, Darth Vader.
Darth Sidious initiates a pre-programmed directive within all clone troopers to kill their Jedi generals, while Anakin kills all the Jedi within the Jedi Temple. Obi-Wan and Yoda are among the few Jedi to survive the extermination and meet up with Senator Bail Organa, who brings them to the Jedi Temple while Sidious, as Palpatine, publicly denounces the Jedi for attempting to overthrow the Republic before reorganizing it into a Galactic Empire with himself as Emperor. Anakin, meanwhile, heads to the volcanic planet of Mustafar where he slaughters the remaining Separatist leaders. Within the Jedi Temple, Obi-Wan witnesses footage of Anakin's massacre as Darth Vader. Yoda tells him to confront and kill Vader, as the good man who was Anakin is no more.
Obi-Wan meets with Padmé, who refuses to believe that Anakin has fallen to the dark side. She travels to Mustafar to be with Anakin, with Obi-Wan secretly stowing aboard. Noticing Anakin's new behavior, Padmé realizes that Obi-Wan was telling the truth. Spotting Obi-Wan within her ship, Anakin accuses Padmé of betraying him and uses the Force to strangle her into a coma. Obi-Wan and Anakin engage in a vicious lightsaber duel across the volcanic facility and over a river of lava. Finally, Obi-Wan gains the upper hand and, acting upon an ill-judged attack by Anakin, swiftly dismembers his former comrade. Anakin slides down a bank of volcanic ash and goes up in flames, while Obi-Wan collects his lightsaber and leaves him to die. Obi-Wan escorts the injured Padmé to the asteroid Polis Massa where he regroups with Senator Organa and Yoda, the latter of whom has gone into self-imposed exile after dueling Darth Sidious to a stalemate, while Sidious finds his apprentice barely alive and takes him away to revive him.
Padmé gives birth to twins, a boy named Luke and a girl named Leia, and dies, but not before insisting to Obi-Wan that there is still good in Anakin. Meanwhile, Sidious has Darth Vader rebuilt in a cybernetic body armor and respirator suit to keep him alive. Vader lets out a scream of agony when he is told by Sidious that he himself killed his wife. With Anakin's children the last hope for the galaxy, Obi-Wan, Yoda and Organa agree that they should be hidden and separate from one another. Leia is taken to Alderaan to be raised by Organa, while Obi-Wan takes Luke to Tatooine to live with his in-law relatives.