On the eve of retirement, Kirk and McCoy are charged with assassinating the Klingon High Chancellor and imprisoned. The Enterprise crew must help them escape to thwart a conspiracy aimed at sabotaging the last best hope for peace.
After an explosion on their moon, the Klingons have an estimated 50 years before their ozone layer is completely depleted, and they all die. They have only one choice - to make peace with the Federation, which will mean an end to 70 years of conflict. Captain James T. Kirk and crew are called upon to help in the negotiations because of their experience with the Klingons. Peace talks don't quite proceed, and Kirk and McCoy are convicted of assassinating the Klingon High Chancellor, and imprisoned on Rura Penthe, a snowy hard-labor prison camp. Will they manage to escape? And will there ever be peace with the Klingons?
After a lunar cataclysm brings the Klingons to their knees, the foreign concept of peace with the Federation may be finally within reach. After 70 years of hostility, the Federation and the Klingon Empire prepare for a peace summit. Ironically, Captain James T. Kirk has been assigned as the first emissary to broker that peace. However, the prospect of intergalactic glasnost with sworn enemies is an alarming one. When the Klingon flagship is attacked and the USS Enterprise is held accountable, the dogs of war are unleashed again, as both worlds brace for what may be their final, deadly encounter.
- The story opens with an immense explosion somewhere in space. Huge shock waves radiate out from the blast site. On board the USS Excelsior, Captain Hikaru Sulu (George Takei) makes an official entry in his log, noting that his mission of cataloging gaseous anomalies in Beta Quadrant is over and they are returning to Earth. The ship is suddenly struck by one of the shock waves from the explosion. Sulu orders his crew to restore control to the ship, which is done quickly. Looking over their scanning equipment, the crew determines that the shock wave originated at the location of the Klingon moon Praxis and that much of the moon is gone. Sulu remarks that Praxis is the primary source of energy for the Klingon Empire, and orders a message be sent stating he and his crew will assist if necessary. They receive an emergency transmission from Praxis showing a Klingon worker consumed in flames. A second message comes from Brigadier Kerla (Paul Rossilli) that acknowledges the explosion (he calls this an incident) and that they do not require assistance from the Federation. He also commands them to remain outside the Neutral Zone. When one of the crew asks if they should report the incident, Sulu replies "Are you kidding?"
On Earth two months later, Captain James T. Kirk (William Shatner), Dr. Leonard McCoy (DeForest Kelley) and Montgomery Scott (James Doohan) attend a top-level meeting at Starfleet Headquarters. They are informed that the Klingon Empire has roughly 50 years of life remaining. Charge of the meeting is turned over to the Federation's special envoy, Captain Spock (Leonard Nimoy). He informs the committee that the explosion of Praxis two months earlier has caused an environmental catastrophe on the Klingon homeworld Qo'noS (Kronos). Pollution of the planet's ozone layer has left Klingon civilization with only 50 Earth years of oxygen. Due to their enormous military budget, the Klingon Empire is unable to reverse the devastation and has turned to the Federation for assistance. However, as Spock notes, assistance cannot begin until a treaty has been negotiated with the United Federation of Planets to cease all hostilities between the two. Acting as the Federation's envoy, Spock had been speaking directly with Chancellor Gorkon (David Warner) of the Klingon Empire to open treaty proposals.
The committee is stunned by the news and debates whether Starfleet will be dissolved. Science and exploration will continue, however, military efforts will see a significant reduction. Admiral Cartwright protests, saying that the Klingons will become the alien trash of the galaxy and that an opportunity exists to bring them to their knees. Spock counters, saying that a peaceful solution is more prudent. In the midst of the debate, it is announced that Kirk will be sent on the Enterprise to the outskirts of Klingon space to escort Chancellor Gorkon's cruiser to Earth for negotiations. Kirk is wholly reluctant, despite Spock's endorsement of him, saying an experienced ambassador should be sent, however, the council leadership ignores him and closes the meeting. After everyone has left the meeting, Kirk confronts Spock, demanding to know why Spock chose him to escort the Chancellor. Kirk has a high distrust of Klingons, who were responsible for the brutal murder of his son, David Marcus. Spock believes that Kirk, though an unlikely candidate for the mission, should still go, saying "Only Nixon could go to China." Kirk also mentions that the Enterprise's crew was due to stand down (retire) in three months.
Kirk gathers his crew and the Enterprise leaves Earth. New to the Enterprise is Lt. Valeris (Kim Cattrall), a Vulcan female officer, who is the first of her race to graduate at the top of her class, having been mentored and sponsored by Spock himself. As the ship races towards the rendezvous point with Gorkon, she and Spock share a ceremonial drink in his quarters and discuss the turning point of Federation relations with the Klingon Empire and their implications. Spock informs her that logic does apply to the events at hand but there must also be some acceptance of faith that the new era will bring peace.
The Enterprise and Gorkon's cruiser, Kronos One, arrive at the meeting point. Kirk hails the Chancellor and invites him and his officers to dinner on the Enterprise that night. Lt. Valeris mentions to Kirk the availability of an on-board supply of Romulan ale, which she suggests might make the evening pass more smoothly. Kirk replies, "Officer thinking, Lieutenant." The Klingons are beamed aboard; the Chancellor has brought his daughter, Azetbur (Rosanna DeSoto), his chief of staff, General Chang (Christopher Plummer) and Kerla. Though both sides are initially pleasant toward each other, and a few toasts to the peace accords and Gorkon himself are made over Romulan ale, the underlying hostility of both sides still permeates the conversation. The Klingons themselves seem particularly fond of Shakespeare; their philosophical arguments about the peace accords are laced with Shakespearean thought. At one point, Chang announces that his people need breathing room, whereupon Kirk mentions that the same thought was expressed by Adolf Hitler in 1938. Azetbur speaks of the Federation being a homo sapiens only club, despite Spock's presence. Gorkon concludes that there is still much work to do. As the Klingons prepare to beam back to their ship, Gorkon informs Kirk he understands his mistrust for Klingons. They leave and the Enterprise crew (literally) breathes a sigh of relief. Chekov (Walter Koenig) mentions that their visitors had terrible table manners and Kirk says their own behavior, as humans, was fairly unacceptable as well.
Resting in his quarters (and making a log note that Romulan ale is now banned from all diplomatic functions aboard the ship), Kirk receives a call from Spock to report to the bridge. Hung over, Kirk meets with Spock, who informs him a huge, unexplained neutron radiation surge has been detected on a scanner. As Kirk and Spock try to find its origin, Kronos One is suddenly hit by a torpedo blast which appears to come from the Enterprise. The Klingon cruiser is hit again and begins to tumble helplessly, losing thruster power and their artificial gravity. On board Kronos One, two figures, wearing Starfleet space suits and magnetic gravity boots, beam aboard and begin to fire upon the Klingon crew with phasers. Several are killed, one is wounded, losing an arm. The assassins move through the ship, finding the Chancellor's chambers. The two Klingons with him are immediately killed, and Gorkon is shot through the chest. The assassins walk back to the transporter pads and beam out, trailing some Klingon blood with them.
Chang hails Kirk and immediately accuses him of the attack on the cruiser. Kronos One moves into an attack position and activates its primary cannon, preparing to fire on the Enterprise. Knowing that the attack would be deadly and spark an interstellar war, Kirk surrenders immediately. He offers to come aboard Kronos One and McCoy volunteers to go as well for medical assistance. As Kirk leaves the bridge, Spock surreptitiously touches his shoulder, placing a small object on his uniform. Kirk and McCoy beam to Kronos One and are escorted by Kerla to the Chancellor, who lies bleeding and dying on the deck. Chang informs them about the assassination and accuses them of lying when Kirk claims innocence. McCoy demands to treat Gorkon and does, however, his unfamiliarity with Klingon internal anatomy prevents him from doing more than reviving Gorkon for a few moments. Gorkon gestures for Kirk to approach him and, putting his hand on the back of Kirk's neck says "Don't let it end this way." He dies. Chang immediately places Kirk and McCoy under arrest for the murder under the Federation's articles of interstellar law.
On board the Enterprise, Uhura (Nichelle Nichols) reports the arrest. Spock assumes command of the ship and orders a general standing down, knowing they cannot attack Kronos One to rescue Kirk and McCoy. Uhura also receives a message from Starfleet to return to Earth immediately, however wishing to investigate the attack on Kronos One and Gorkon further, Spock discreetly orders Uhura to report that the ship is experiencing multiple malfunctions and cannot return until they are repaired.
On Earth, the Federation President meets with several other council members about the incident. Among them is the Klingon ambassador, who defends his government's arrest of Kirk. The Klingon ambassador also cites Federation interstellar law, as Chang did. Vulcan and Romulan ambassadors Sarek (Mark Lenard) and Nanclus (Darryl Henriques) agree, as does the president, who does not want to provoke the already delicate relations with the Klingon Empire. A daring rescue plan, proposed by Colonel West (Rene Auberjonois), is dismissed by the president as well. In Gorkon's place, Azetbur is appointed chancellor and speaks directly to the president, saying Kirk and McCoy will stand trial on Qo'noS. She also affirms her reluctance to attend the peace accords, but agrees, saying that the location must be kept secret and that any attempt to rescue Kirk and McCoy will be an act of war.
The trial begins; the prosecuting attorney is Chang himself, while Kirk and McCoy are defended by Colonel Worf (Michael Dorn). Chang delivers the charges, that Kronos One was fired upon, the assassins came from the Enterprise and that Kirk ordered the attack. Though Worf successfully dismisses the final charge, Chang is still able to lay the conduct of the two assassins on Kirk, saying, as captain, he is responsible for the conduct of the crew under his command, one that Kirk does not deny. When McCoy is questioned about his attempt to revive Gorkon, Chang verbally attacks him, challenging his medical expertise based on McCoy's age. He also cites the fact that McCoy, along with all the other dinner guests, consumed Romulan ale that may have affected his ability to help the Chancellor. The most damning evidence that influences the trial is Kirk's own words, possibly stolen from his personal log, where he stated "I've never trusted Klingons, and I never will. I can't forgive them for the death of my boy." The jury and court are swayed and Kirk and McCoy are found guilty. Though the Klingons want the death penalty for Kirk, in the interest of continuing peaceful negotiations with the Federation, the judge sentences the two to life imprisonment on the Klingon penal colony, Rura Penthe ("The Aliens' Graveyard"), a remote and frozen asteroid deep in Klingon space, where they will mine dilithium for the rest of their lives along with thousands of other Klingon prisoners.
On the Enterprise, at Spock's request, the bridge crew watches a video of the torpedo hits to Kronos One. They determine that, though the memory banks of the Enterprise show two torpedoes had been fired and that all the torpedoes they were carrying before the attack have been visually accounted for, the shots must have come from another ship. The only ship capable of remaining undetected would be one with a cloaking device, a Bird-of-Prey, which cannot fire while cloaked. Spock ascertains, through the logical statement "once you eliminate the impossible, whatever remains, however improbable, must be the truth" that the Bird-of-Prey that fired on Kronos One can fire while cloaked. After further deduction, the crew knows what they must search for: the two pairs of magnetic gravity boats worn by the assassins. The crew begins to search every corner of the ship; as they do, they are continually contacted by Starfleet and ordered to return to Earth. Spock orders Scotty to report that the Enterprise is experiencing a warp drive malfunction. When Scotty begins to protest, Spock slyly but firmly informs them they need more time to search the ship. Scotty heartily says it could take weeks to repair. Chekov later finds dried Klingon blood on the transporter pads and Spock says they will also search uniforms. A pair of gravity boots are found in the locker of Crewman Dax, however his feet are largely different from human feet and could not possibly fit the boots.
Meanwhile, Kirk and McCoy arrive on Rura Penthe. They are informed by the facility's cantankerous Klingon warden that nothing can survive on the surface due to extremely cold temperatures, and a prisoner is cruelly thrown outside to prove the warden's point, freezing in mere minutes. A magnetic field above the asteroid prevents any unauthorized beaming to a ship. In the depths of the mine, Kirk is threatened by a large alien who demands his coat. Another prisoner, Martia (Iman), appears and orders the thug to back off. Kirk later finds himself in a fight with another huge alien who is easily winning the battle. Kirk kicks the thug in the knees and he falls down defeated. When he remarks he was lucky, Martia informs him that he kicked the creature in the genitals. Later, after they go to bed, McCoy relates their plight to the no-win scenario of the Kobayashi Maru test. Kirk theorizes that the incidents that led them to their imprisonment may have something to do with others who fear the peace accords with the Klingons if the Neutral Zone between the Klingon Empire and Starfleet was weakened or dissolved. Suddenly, Martia appears and offers Kirk the chance to escape from the planet. The next morning, they go to a meeting place arranged by Martia, but do not see her. However, she is there, in the disguise of a large, hairy and ape-like alien. She later changes to the form of a young human girl, allowing her to slip out of her shackles. She takes Kirk and McCoy through a hidden tunnel that leads to the frozen surface of the planet and gives them warm winter clothing. They begin a lengthy march that will put them beyond the magnetic field covering the prison.
Back on the Enterprise, the signal from the device that Spock secretly placed on Kirk, a viridium patch, appears on a scanner and they set a course for Rura Penthe. In order to evade Klingon security outposts, and unable to use a universal translating device, Uhura must speak in Klingon. She is able to deceive a sleepy guard at a security outpost and the Enterprise continues to Rura Penthe. Martia provides a flare for building a fire. Kirk says he recognizes her as a chameloid, a shape-shifting species that were supposed to be mythical. Kirk also hits her, knowing she plays to turn them over to the warden, who will execute them both for attempted escape and give Martia a full pardon. Martia changes into a likeness of Kirk himself and the two fight. The warden and several guards appear. After a few moments of confusion about the identity of the real Kirk, insulted by the real Kirk, the warden vaporizes Martia with a blaster and is about to inform Kirk who is behind the plot to kill him when he and McCoy are suddenly beamed to the Enterprise. The ship streaks away from Klingon space.
Spock brings them both up to date on his theory. As they make their way to the bridge, they find two crew members' bodies lying in a passageway, both killed by stun shots at close range. Scotty runs up, having found the missing uniforms with Klingon blood, which belong to the two dead crewmen. Kirk and Spock have a quiet discussion and arrange a trap for the crew members' killer. A ship-wide announcement is broadcast, saying statements will be taken from the dead crewmen in sickbay. Their killer goes there and finds Kirk and Spock posing as the corpses. They discover that the killer is Valeris and Spock is visibly furious.
On the bridge, Kirk and Spock interrogate Valeris and discover she is part of a conspiracy to sabotage the peace accords and had stood outside Kirk's quarters, recording the log entry used as evidence at his trial. She refuses to reveal the names of her cohorts; Spock performs a very intensive mind-meld and finds out that Admiral Cartwright, General Chang and Romulan Ambassador Nanclus and are also part of the conspiracy. However, she does not know where the peace conference will take place. The Enterprise hails the Excelsior and Sulu informs them that the peace conference will be held on the planet Khitomer. Valeris also reveals that there is only one Bird-of-Prey that can fire while cloaked, a prototype. Detecting it will be difficult, however Kirk orders the crew to set course for Khitomer, after warning Sulu about the evasive ship. Sulu says reaching them in time will be difficult but he agrees to help.
Meanwhile, the historic peace conference gets underway at Camp Khitomer. Several of the conspirators are present, one of the Klingons in the audience leaves the meeting hall and takes up a position above the speaker's podium and assembles a Klingon sniper rifle. The Enterprise arrives on Khitomer and is quickly hailed by Chang on the prototype Bird-of-Prey. He taunts Kirk with Shakespearean dialog, saying that Kirk prefers war to peace and opens fire on the Enterprise. The Enterprise takes heavy damage and her shields quickly collapse. The Excelsior arrives shortly after the battle begins and provides distraction for Chang. In the meeting hall on Khitomer, Azetbur gives an impassioned speech about her father's efforts to secure peace. In space, the Bird-of-Prey fires several more severely damaging blasts at the two Federation starships. Spock suddenly has an idea; he mentions that the Bird-of-Prey expels gas as its exhaust. Uhura suggests they use the equipment they have on board for studying gaseous anomalies that could detect the exhaust Spock mentions and Spock and McCoy equip a photon torpedo with the components. The torpedo is fired and homes in on Chang's ship and scores a direct hit, crippling its cloaking device. Both the Enterprise and the Excelsior destroy the prototype with photon blasts.
On the planet, the Federation President takes the podium while the Klingon sniper aims his rifle at him. Having beamed down with Spock, Valeris and Scotty, Kirk rushes the stage and pulls the president out of the way just as the sniper shoots. Seeking another target, as the sniper points his rifle at Valeris, Scotty bursts into the room and shoots him. He falls through a glass window and onto the hall floor. The sniper is actually Colonel West, wearing a Klingon mask. Kirk explains that they have evidence of the plot and that those involved were frightened of the potential changes that would result.
Later, the Enterprise and the Excelsior both head out into deep space from Khitomer. They communicate one last time with Sulu aboard his ship before he takes another course. They receive a transmission from Starfleet ordering them to return to Earth for decommissioning. Spock suggests their response would be "Go to hell." Chekov asks for a course heading and Kirk says "Second star to the right and straight on 'til morning." Kirk notes in his log that this is the final voyage of the Enterprise under his command, but there will be others who will take up his mission to go where no man, or no one, has gone before. The Enterprise goes to warp speed and disappears.
Before the closing credits roll, the signatures of the principle cast members appear on the screen one at a time.