Defeat and Victory

On Stardate 3372.7, Mr. Spock, first officer of the starship USS Enterprise, abruptly requests a leave of absence to his home planet of Vulcan after displaying irrational behavior for several days. Captain Kirk and Dr. McCoy witness one of Spock's outbursts, including the throwing of a bowl of Vulcan plomeek soup specially prepared for him by Nurse Chapel, and McCoy agrees Spock needs some "time off". 
Kirk is baffled by the strange behavior and Spock's unwillingness to tell him more than "I need rest", but honors Spock's request and diverts the Enterprise to Vulcan. Soon however, Kirk receives a priority signal with orders to proceed to Altair VI to represent the Federation at an inauguration ceremony for the planet's new president. Kirk tells Spock his leave will have to be delayed. Later, Kirk asks Mr. Chekov how long it would take to get to Altair if they diverted to Vulcan just long enough to drop off Mr. Spock; Chekov replies that Spock has already ordered a course change to Vulcan. 
Kirk confronts Spock, who says he has no memory of having changed the order. Kirk orders him to report to sickbay for a full examination. Once there, Dr. McCoy discovers Spock's blood chemistry is extremely active and has the presence of unknown hormones. If the condition persists, Spock will die in eight days from the physical and psychological stress. Spock does not wish to discuss what is currently affecting him, but Kirk demands an explanation. 
Seemingly embarrassed, Spock informs that his condition is called Pon farr, a very personal biological syndrome that all Vulcan males painfully endure periodically throughout their adult life. During this time, they must join with their wives, or die. Spock compares his need to return to Vulcan to the need for eel birds of Regulus to return every eleven years to the caverns where they hatched, and also to salmon of Earth who must return to the stream where they were born to spawn. Kirk gets the idea that it is essentially Spock's mating season. 
Kirk contacts Admiral Komack at Starfleet Command Sector 9, and requests permission to divert to Vulcan. The Admiral denies permission, but Kirk ignores the order, arguing there are already two other starships attending the Altair VI ceremony. Spock seems to calm down once he learns Kirk is doing what he can. 
The Enterprise finally arrives at Vulcan, and Spock invites Kirk and Dr. McCoy to accompany him to the surface. Once there, Kirk comments on Vulcan's extremely harsh environment and its atmosphere which is thinner than Earth's. 
Spock explains to them that Vulcans are married as children with the understanding that they will fulfill this commitment when they become adults. His bride T'Pring, who was betrothed to him at the age of 7, awaits him. He must enter Kunat kalifee, his family's traditional place of the Vulcan marriage ceremony. 
T'Pau, a highly respected member of Vulcan society, and best known as the only person to ever turn down a seat in the Federation Council, arrives to conduct the ceremony. 
T'Pring arrives accompanied by Stonn, a pure-blooded Vulcan, who is obviously her lover. She invokes kal-if-fee, her customary right to a physical challenge between Spock and Stonn. But instead, she picks Kirk to be her challenger to fight Spock. The duel pains Spock, and he asks that T'Pau forbid it because Kirk "does not understand, he does not know", but T'Pau allows it. She tells Kirk to decide, telling him another champion will be selected if he declines. Kirk accepts the challenge, thinking he can let Spock win — then discovers that this is a fight to the death. 
Regardless of Spock's condition, he displays superior strength and agility. Kirk is weakened by Vulcan's heat and thinner atmosphere and must struggle harder against Spock's strength. McCoy objects, telling T'Pau that Kirk is seriously disadvantaged, and suggests he inject Kirk with a tri-ox compound to compensate. T'Pau allows the injection. The combat continues and Spock garrotes Kirk with a traditional weapon, at which point McCoy pronounces the Captain dead and has his body beamed back to the Enterprise. 
With the battle over, Spock now realizes what has happened. He gives up his claim on T'Pring and sadly returns to the ship, though not before questioning T'Pring on her choice of Kirk as her champion; in a display of logic that impresses Spock in its flawlessness, T'Pring explains that with Spock's name now near-legendary among their people, she developed a mutual attraction with Stonn rather than becoming the consort to such fame. However, since she could only legally divorce Spock through the kalifee, and allowing Stonn to take the challenge as her champion would risk losing him, she instead chose Kirk, knowing that regardless of the outcome, she and Stonn would be together - as Spock would either be dead or in prison for killing Kirk. 
On the ship, Spock announces his intention to resign from Starfleet and submit himself to whatever consequences await him for killing Kirk. However, he finds his Captain alive and well, and expresses overt joy (unusual for a normally emotionless Vulcan) in the full witness of McCoy and Chapel. McCoy and Kirk then explain that McCoy actually injected the Captain with a neuroparalyzer drug that simulated death but merely knocked him out. Spock says that when he thought he had killed the Captain, he found that he had lost all desire for T'Pring, and the madness was gone. Furthermore, Kirk is let off the hook for disobeying orders when Starfleet retroactively grants permission to divert to Vulcan at T'Pau's request.
The opening crawl reveals that the Galactic Empire has been working on the construction of a new armored space station which is to be even larger and more powerful than the first Death Star. Jedi Knight Luke Skywalker, Chewbacca, Lando Calrissian, Princess Leia Organa, C-3PO, and R2-D2 return to Tatooine in an attempt to rescue Han Solo from the gangster Jabba the Hutt. Leia, disguised as a bounty hunter, attempts to secretly free Solo, who is still encased in carbonite. She succeeds, only to be discovered and captured by Jabba, who makes her his personal slave. Several days later Luke arrives to make one final plea to Jabba to release Solo. Luke is then captured by Jabba's guards and dropped into a dungeon to battle a rancor. After defeating the rancor he is sent along with Han Solo and Chewbacca to the Great Pit of Carkoon to be slowly consumed by the Sarlacc. With the help of R2-D2, Luke escapes and a large battle erupts; during the chaos, Leia strangles Jabba to death with her slave chains, and Han accidentally knocks Boba Fett, the bounty hunter who brought him to Jabba, into the pit where he is eaten alive by the Sarlacc. Following this, Luke blasts Jabba's sail barge with its own deck cannon, and all of the heroes manage to escape before it explodes. 
Luke then returns to Dagobah to complete his Jedi training. However, upon arriving, he finds Yoda is languishing. Yoda tells Luke that no other training is required, but that he will not truly be a Jedi until he confronts Darth Vader who, Yoda confirms, is Luke's father. Yoda then dies, but not before telling Luke that "there is another Skywalker". The spirit form of Obi-Wan Kenobi then appears and confirms that Vader was once Anakin Skywalker, a former Jedi who was turned to the dark side of the Force. Though he initially seemed to imply that Vader was merely another Jedi who betrayed and murdered Anakin, Obi-Wan explains that Vader truly did this in the sense of the dark side consuming Anakin's mind, apparently destroying the good man who was Luke's father and replacing him as Vader. Luke asks Obi-Wan about the "other" Skywalker Yoda mentioned—Obi-Wan reveals that this "other" is his twin sister, hidden from Anakin and separated at birth to protect them both from the Emperor. Using his intuition, Luke quickly deduces that, to Obi-Wan's confirmation, his sister is Leia. 
Meanwhile, the entire Rebel Alliance is meeting to devise an attack strategy. As part of the attack, Han is elected to lead a strike team to deactivate the shield generator on the forest moon of Endor which is projecting a protective shield up to the orbiting and incomplete Death Star. Luke, having returned from Dagobah, joins him and Leia for this mission; however, he soon fears that, after sensing Vader's presence within the nearby Imperial Fleet, his own presence may endanger the mission. On Endor, Luke and his companions encounter a tribe of Ewoks, primitive yet intelligent indigenous forest creatures of Endor. With the help of C-3PO, whom the Ewoks believe is a god, they are able to forge an alliance with the forest creatures. Later, Luke decides that the time has come for him to face Vader. He confesses to Leia the truth about her and Vader, and that he has to try to save the man who was once their father. He surrenders peacefully to Vader and unsuccessfully tries to convince his father to abandon the dark side. They go to the Death Star and meet the Emperor, who reveals that he knew of the attack before, and that the Rebel Alliance is walking into a trap. On the forest moon, the Rebels – led by Solo and Leia – enter the shield generator control facility only to be taken prisoner by waiting Imperial forces. Once they are led out of the bunker, however, the Ewoks spring a surprise counterattack. A desperate ground battle begins with the Rebels and Ewoks fighting the Imperial forces. The Rebels eventually gain the upper hand, due in large part to a stolen Imperial AT-ST Walker. 
During the strike team's assault, the Rebel fleet, led by Lando, emerges from hyperspace for the battle over Endor, only to discover that the shield of the Death Star is still functioning. An intense space battle takes place as the Rebel fleet battles to give the surface party more time to complete their mission of deactivating the Death Star's shield. During the battle, the Death Star is revealed to be operational; its superlaser is fired at the Rebel fleet and obliterates two Rebel star cruisers. This forces a rethinking of strategy and the fleet closes with the Imperial star destroyers to prevent the superlaser from firing on the Rebel fleet. 
On the Death Star, the Emperor tempts Luke to give in to his anger. A ferocious lightsaber duel erupts between Luke and his father. In the midst of combat, Vader reads Luke's feelings and learns that Luke has a twin sister. When Vader toys with the notion of turning Leia to the dark side, Luke gives in to his anger and brutally overpowers his father, eventually slicing off Vader's robotic right hand. However, despite the Emperor's goading, Luke refuses to kill his father, realizing that he is traveling down his father's path towards the dark side. He declares himself a Jedi, like his father before him. Upon realizing that Luke cannot be turned, the Emperor tortures and slowly kills him with Force lightning; in unspeakable pain, Luke begs his father for help. Facing a moral crisis as he sees his son dying before his own eyes, Vader finally repents in return of his former self, Anakin Skywalker, and turns on the Emperor, grabbing him over his shoulder and throwing him down a reactor shaft to his death. At the same time, however, the life support system in his suit is damaged beyond repair by the Emperor's lightning. Moments from death, he begs Luke to take off his breath mask to see him with his own eyes. Luke does so, and finally sees his father's true face: that of a pale, withered man ravaged by the dark side. He entreats Luke to leave him and save himself, and to tell Leia that there was some good left in him after all. With those last words, Darth Vader/Anakin Skywalker dies, finally at peace. 
Back on Endor, the strike team finally destroys the shield generator. The Rebel fleet seizes the opportunity to launch a final assault on the Death Star in space. Lando leads Wedge Antilles and his fighter group into the interior of the Death Star and they fire at the main reactor, causing its collapse. Luke escapes the Death Star with his father's body in an Imperial shuttle. Moments later, Wedge in his X-Wing and Lando in the Millennium Falcon emerge from the Death Star as well, just as it explodes. Back on Endor, Leia senses that Luke had escaped the station before it exploded. Han believes that she loves Luke and is prepared to let her go, but Leia reassures Han of her love for him and reveals (to his surprise and relief) that Luke is actually her brother. That evening, Luke cremates the remains of his father in his black armor on a funeral pyre on Endor. 
The entire galaxy celebrates the fall of the Empire and the Rebellion's victory. On Endor, Luke, Leia, Han, Lando, and the rest of the Rebellion, along with the Ewoks, celebrate the victory as well. During the celebration, Luke catches sight of the spirit figures of Obi-Wan Kenobi, Yoda and the redeemed Anakin Skywalker, who watch over them with pride.