Day of Glory

After failing to persuade the Halkan Council to allow the Federation to mine dilithium crystals on their planet, Captain James T. Kirk, along with Dr. McCoy, Scotty, and Lt. Uhura, return to the Enterprise. An unexpected ion storm causes a transporter malfunction, and the landing team beams aboard an unfamiliar Enterprise.
The group realizes something is amiss as they arrive on the transporter pad: a goateed Mr. Spock viciously tortures the transporter operator, Lt. Kyle, for carelessness in nearly losing the ship's captain. (Low ranking crew members carry "agonizers", which superior officers use to punish them for dereliction of duty.) Kirk deduces that they must have switched places with their mirror-universe counterparts, and the landing party from this universe must now be aboard his Enterprise, and that his landing party must impersonate their counterparts until they can find a way home. In this alternate universe, the USS Enterprise is called an "Imperial Starship" or ISS Enterprise, and a brutal Terran Empire has replaced the Federation. Officers rise in rank by assassinating their superiors (as Kirk discovers when Chekhov nearly succeeds in assassinating him), and as a result all high ranking officers must hire a personal bodyguard. Uniforms in this alternate universe are very different; sidearms and daggers are standard issue, while the clothing itself is much more revealing. Torturing subordinates is an acceptable form of discipline in this alternate universe.
On board on the USS Enterprise Mr. Spock notices the changed personalities of the landing party and orders security to take them to a holding cell. The mirror Kirk tries to bribe Spock with rewards of "a command of (his) own" if he's freed but Spock simply replies "fascinating" and continues investigating. Spock comes to the same conclusion as Kirk: the ion storm must have opened a barrier between parallel universes and the two landing parties have switched places.
Back on the ISS Enterprise, Kirk goes to the captain's quarters on this ship, which are quite different from his own. He discovers that the mirror-Kirk has been ordered to annihilate the Halkans if they refuse the Empire's "request" to mine dilithium, and horrified, Kirk studies his counterpart's records further, In this universe, "Kirk" gained command of the ISS Enterprise by assassinating Captain Christopher Pike and was responsible for massacring 5,000 colonists on Vega IX, among many other atrocities.
Mirror-Spock informs Kirk that the ship is ready to attack the Halkans. Desperately, Kirk orders a delay in the attack for 12 hours. This piques mirror-Spock's curiosity, but he obeys the order; he does report the suspicious activity of his Captain to the Imperial Command, and receives orders to kill Captain Kirk if he does not carry out the order to destroy the uncooperative Halkans.
Having failed to sabotage the weapons systems, Scotty and McCoy work secretly to figure out what happened with the transporter. While Scotty is finding a way to return them to the correct universe, Kirk goes to his quarters and meets the beautiful Lieutenant Marlena Moreau, who refers to herself as the "Captain's Woman". It appears that female crew members may attach themselves by agreement to particular men - Marlena is evidently tiring of her Kirk. Marlena shows Kirk the Tantalus Field, a device in the captain's quarters which can secretly monitor anyone on the ship and "eliminate" them. When he prevents her from eliminating the mirror-Spock, she realizes something is wrong--her Kirk would not have hesitated.
Kirk stalls the mirror-Spock while his crew search for a way home, but Spock is suspicious. Spock, not wanting command of the ISS Enterprise as it would make him an instant target of assassination, decides instead to study the Captain as long as he can.
Scotty has, with the aid of McCoy, rigged up the necessary connections to make a return switch. Mirror-Sulu, the security chief, is distracted from his monitors at the vital moment of connection by Uhura seeming to encourage his previously-rejected amorous advances. The party reaches the transporter room, but the mirror-Spock confronts them and leads them to sick bay. In the ensuing fight, Kirk knocks the Vulcan and the mirror-Sulu unconscious. (Marlena has "eliminated" Sulu's thugs with the Tantalus Field.) Uhura, Kirk, and Scotty head for the transporter room again while McCoy stays behind to make sure that mirror-Spock is all right. In the transporter room they meet Marlena, who now knows the facts and asks them to take her with them. Kirk refuses on the grounds that the energy is set for four people. Marlena persists and is disarmed by Uhura.
Mirror-Spock suddenly comes to and quickly mind melds with McCoy in order to read his mind. He discovers the switch, and offers to operate the transporter so that the entire landing party may return to their own universe. This convinces Kirk that this universe's Mr. Spock is still an ethical Vulcan guided by logic. He suggests to mirror-Spock that a Federation-like system is more logical than the ruthless barbarian Empire. Spock objects that one must have the power, and Kirk informs him of the Tantalus Field. Mirror-Spock agrees to consider the idea. (Marlena is presumably now on his side.)
On board the USS Enterprise, Spock decides to attempt the beaming sequence at the same time the ISS Enterprise attempts theirs. The switch is successful. As the episode ends, Kirk meets his own universe's Lieutenant Marlena Moreau, who is quite a different girl from what he experienced her to be in the other universe. Kirk tells Spock that Moreau "seems like a nice, likable girl" and that he thinks they "could be friends". The real Spock also comments that the ruthless attitude of the Mirror Kirk, Dr. McCoy, Scotty, and Uhura were refreshing, and "the very flower of humanity".
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.