When a plague in the densely populated Rachelis System races out of control, help from the U.S.S. Enterprise is enlisted in the medical emergency. But while preparing to transport samples of a deadly plasma plague from a Federation research station to a site where a suitable antidote can be developed, the crew is stunned by an unexpected announcement: Counselor Troi is pregnant. According to Troi, a glowing white light impregnated her while she was asleep. Dr. Kate Pulaski, the ship's new Chief Medical Officer, confirms Troi's prognosis and reports that the fetus will reach full term within 36 hours. Not knowing the true origins or intent of this mysterious child, Picard puts the crew on security alert. But when Troi gives birth to a boy named Ian, he appears to be completely harmless - although he amazes his mother and the crew when he grows from an infant to an eight-year-old in one day.
While en route to the Morgana Quadrant, the U.S.S. Enterprise is engulfed by a mysterious 'hole' having no dimensions and void of all energy and matter. Captain Picard is perplexed by this mysterious oddity which cannot be measured or defined in human terms, and the crew is caught in a trap which, by their standards, does not even exist. The crew is then confronted by a giant human eye which peers in at them through the main view screen. The being, calling Itself Nagilum, explains that he is using the Enterprise in an experiment to study human life -- specifically, the many ways in which humans die.
Geordi summons Data to the holodeck, where they travel back to Victorian London to solve one of Sherlock Holmes's mysteries. But the trip turns out to be a brief one because Data can solve the crime with very little effort. Dr. Kate Pulaski challenges Data to solve a real crime, a la Sherlock Holmes. Geordi orders the computer to present Data with an original mystery and an opponent who could defeat him. Kate joins Data and Geordi as they return to London, via the holodeck. But their game turns serious when Kate is kidnapped by Holmes' arch-enemy, Professor James Moriarty. Although they track down Kate's location, they are unable to retrieve her because Moriarty has taken control of the holodeck computer.
While traveling through the Omega Sagitta Twelve System, the U.S.S. Enterprise aids a disabled cargo ship and plays host to its sole occupant, Captain Okona. Once on board the Starship Enterprise, the handsome, roguish Okona charms the crew -- particularly the women -- with his quick wit and mischievous manner. Data, however, is unable to understand Okona's jokes and looks to Guinan and the Holodeck for lessons in human humor. Meanwhile, two small interplanetary vessels lock their lasers on the U.S.S. Enterprise, demanding Okona's surrender. First, Debin accuses Okona of getting his daughter, Yanar, pregnant; then Kushell, with his son Benzan at his side, charges the dashing Captain with stealing his nation's prized Jewel of Thesia.
The U.S.S. Enterprise is unexpectedly diverted to the Ramatis star system to transport a famous mediator named Riva to the site of a bitter planetary conflict on Solais V. To the surprise of the away team, headed by Captain Picard, it soon becomes apparent that Riva is deaf. Although he can understand what the crew is saying by reading their lips, his only way of communicating is through the Chorus, a group of three people who not only possess a distinctive aspect of Riva's personality, but can read the mediator's thoughts telepathically and translate them into words. En route to Solais V, Troi and Riva develop a strong mutual affection. Left alone together, Riva communicates his loving feelings toward Troi using thoughts and crude sign language. Arriving at the war-torn planet, Riva, his Chorus and the away team prepare to meet with the leaders of the centuries-old dispute. But when the combatants face each other to begin the peace talks, a dissident soldier opens fire with his weapon, killing Riva's Chorus. The away team and Riva are quickly beamed back aboard the U.S.S. Enterprise before more harm is done. The mediator now must decide to return home or try and continue his mission.
The U.S.S. Enterprise races toward a remote planet on a top priority mission to provide medical aid for Dr. Ira Graves, one of the greatest living human minds. Graves' young assistant, Kareen Brianon, has summoned for help against Graves' wishes. An away team, led by Data, beams down to assist the dying Graves. Data develops a particularly strong rapport with the brilliant scientist, who is bravely enduring the final stages of a terminal disease. Shortly after Graves tells Data of his remarkable ability to transfer human knowledge into a computer, he dies.
An emergency call for help from a Federation supply ship sends the U.S.S. Enterprise racing on a course to determine the nature of the crisis. Upon visually scanning the bridge of the U.S.S. Lantree, the crew is shocked to learn that everyone on the troubled vessel is dead. Dr. Pulaski determines that the crew members, who had been examined and found to be in perfect health eight weeks earlier, have all died of old age. The Lantree is immediately placed under quarantine and the U.S.S. Enterprise heads toward the ship's last port of call, the Darwin Genetic Research Station, to warn them of the potential danger. Unfortunately, the U.S.S. Enterprise discovers that the residents of the Darwin Station are suffering from the same mysterious affliction. Picard is asked to evacuate the children of the station, who have been engineered to become super-specimens through genetic research. Although the children have been kept in isolation and show no signs of infection, a cautious Picard allows Pulaski to examine just one child until the nature of the virulent disease can be determined. When Dr. Pulaski is also infected, the crew of the Enterprise must find a cure within days.
A special exchange program brings a Benzite named Mendon aboard the U.S.S. Enterprise and gives Riker the opportunity to become the first Federation officer to serve on board a Klingon ship. Riker's preparations for his assignment include a lesson from Lt. Worf about Klingons, who still maintain the barbaric view that brute strength rules. The lesson is put to immediate use on board the Klingon cruiser Pagh when First Officer Riker must overpower the Second Officer when he questions Riker's authority and loyalty. Meanwhile, the U.S.S. Enterprise discovers that a virulent strain of bacteria is eating away at the hulls of both their ship and the Klingon vessel. As the U.S.S. Enterprise plots a course to intercept and warn the Pagh, the Klingons discover the bacteria and mistakenly believe the starship is responsible for it. Unable to communicate with the cloaked Pagh, the U.S.S. Enterprise becomes concerned and raises its shields, which the Klingons immediately interpret as an act of aggression.
When the U.S.S. Enterprise arrives at a newly established Starbase, Data is ordered to serve under Captain Bruce Maddox, who wishes to disassemble and study him so that more androids can be made for Starfleet's use. But after Data learns that Maddox may not be able to reassemble him, he refuses to submit to the procedure. When Captain Picard is unable to have the orders changed, Data's only option is to resign from Starfleet. His decision to resign, however, is challenged by Maddox on the basis that Data is not a person with rights, but property of the Federation.
The U.S.S. Enterprise is assigned to escort a young girl and her guardian from the planet Klavdia III, where they have lived almost all of the girl's life, to Daled IV, the planet she was born to rule. The sixteen-year-old Salia has a chance encounter with Wesley, who is instantly and obviously smitten with her, much to the dismay of the girl's overprotective guardian Anya. After a short lesson in love from Guinan and Riker, a nervous Wesley calls on Salia in her quarters, where he introduces her to Thalian chocolate mousse. All the while, Troi is concerned that the emotions she senses from the new passengers don't seem to fit who they are.
The Enterprise enters the Neutral Zone in response to a desperate plea for aid from the U.S.S. Yamato, which has been crippled by a series of dangerous, inexplicable malfunctions on its voyage to the homeland of the Iconians, an extinct civilization. When the U.S.S. Yamato's captain tries to explain his mission to Picard, the transmission breaks up and the U.S.S. Yamato suddenly explodes.
In an unmapped solar system, the U.S.S Enterprise discovers a jagged chunk of metal bearing a United States Air Force insignia. The Away Team beams down to a building on a nearby planet, hoping to find a connection between the structure and the ship fragment. When Riker, Worf and Data materialize in front of a revolving door that leads them into the casino of the Hotel Royale, their communication with the U.S.S. Enterprise is suddenly cut off. While the Away Team searches for an exit, the drama of a bellboy preparing to fight an evil gambler for the woman he loves unfolds before them.
When the U.S.S. Enterprise encounters a Federation shuttlecraft cartwheeling out of control through space, the starship pulls it into the shuttle bay. Riker discovers that the shuttlecraft belongs to the U.S.S. Enterprise, and Dr. Pulaski finds an unconscious double of Picard inside. Captain Picard accompanies his double to sickbay, where Troi explains that the double really is Picard, but from another time.
When Riker is offered a captain's position on the Starship Dreadnaught, the U.S.S. Enterprise heads for Starbase Montgomery so he can be briefed on the assignment. Arriving at the Starbase, Riker is visibly shaken when his father, Kyle, whom Riker hasn't seen in 15 years, is beamed aboard to brief him. Meanwhile, Worf is showing increased hostility toward the crew for no apparent reason. Wesley's investigation into the cause of Worf's uncharacteristic behavior soon reveals that he is feeling culturally isolated because it is the tenth anniversary of his Age of Ascension, a ritual marking a new level of Klingon spiritual attainment. To help Worf celebrate his anniversary, Data, Geordi and Wesley surprise him by recreating a Klingon ritual chamber in the holodeck.
Unbeknownst to the crew, Data has become pen pals with a little girl named Sarjenka who lives on Drema Four, one of the planets under investigation. When Data tells Picard of his communications with Sarjenka, he learns that her planet is in danger of imminent self-destruction as a result of growing stresses beneath its surface. Meanwhile, to help further Wesley's education as a Starfleet Ensign, Riker puts him in charge of the mineral surveys which will determine what's causing the quakes and volcanic eruptions on Drema Four. Against his better judgment, Wesley allows the older crew members under his command to talk him out of ordering a detailed and time-consuming analysis. Later, a discussion with Riker gives Wesley the confidence to order the tests, which soon reveal the cause of the geological disturbances.
Immediately upon arriving in a new galaxy, the U.S.S. Enterprise encounters an alien ship. Suddenly, two Borgs - part organic and part artificial beings -- appear in the Main Engineering room. Unfortunately, the U.S.S. Enterprise's defenses are helpless against the powerful aliens, who begin draining information from ship's computers. Then, having surveyed the ship's weakened defensive capabilities, the Borg vessel demands the surrender of the U.S.S. Enterprise. When Picard refuses, a short but fierce battle ensues, leaving both ships badly damaged and 18 Enterprise crew members dead. Desperate to learn more about this seemingly invincible enemy, Picard sends an Away Team to investigate the Borg ship, which is controlled by the collective minds of all the Borgs, rather than by an individual leader.
In order for Wesley to complete his Starfleet exams, he must travel to Starbase Scylla 515. He is unexpectedly joined on his trip by Captain Picard, who has been ordered by Dr. Pulaski to undergo a cardiac replacement operation. While Picard and Wesley are away, the crew responds to a distress call from the Pakleds, a race of lethargic humanoids. It seems that their ship, the Mondor, requires extensive repairs. To help expedite the process, Riker beams Geordi aboard the Pakled vessel. Sensing that the Pakleds' intentions are less than friendly, Troi expresses concern for Geordi's safety. After making the necessary repairs, Geordi prepares to return to the U.S.S. Enterprise, but he is suddenly disarmed by the Pakleds, who refuse to release him until Riker surrenders all of their computer information.
In response to an urgent distress signal, the U.S.S. Enterprise ventures into the Ficus Quadrant to save the Bringloidis, a society whose planet is about to be destroyed by stellar flares. Upon assessing the situation, Riker beams aboard the entire Bringloidi civilization, which consists of about 200 humans and animals, led by a jovial man named Danilo Odell and his head-strong but beautiful daughter Brenna. Picard soon learns that the Bringloidis had traveled from earth years ago with a second colony of humans. Not interested in remaining on Bringloid, the other group dropped off Danilo and his people and moved on to an unknown destination. Suspecting that the second colony might also be in danger, Picard engages the crew on a search, which leads to the planet Mariposa. When an Away Team beams down, they learn that the entire Mariposan society is composed of clones made from the five crew members who survived their ship's crash landing. Suffering from a degenerative condition known as Replicative Fading, the Mariposans ask the U.S.S. Enterprise officers to donate fresh DNA so they can clone strong new citizens. When Riker and Dr. Pulaski refuse their request, the Mariposans render them unconscious and take the valuable cells from their bodies.
While transporting delegates to a special Federation conference on Pacifica, the U.S.S. Enterprise picks up two representatives from the newly discovered planet of Antede III. Unaccustomed to space flight, the aliens arrive on the ship in a self-induced coma to deal with the trauma of their voyage. En route to the conference, Picard and the crew are taken aback by the unexpected arrival of Mrs. Troi, who also happens to be on her way to the meeting on Pacifica. Upon finding himself the object of Mrs. Troi's passions, Picard turns to Counselor Troi for advice. She explains that her mother is at 'the phase,' a mid-life period when a Betazoid woman's sex drive increases tenfold! Reluctant to reject Mrs. Troi's amorous advances, Picard decides to seek refuge from her in the Holodeck. As a result, she redirects her search for a mate to the other men on the U.S.S. Enterprise. Her 'manhunt' ends on the Bridge when Mrs. Troi eyes Riker and announces to the crew that the two will soon be wed.
The U.S.S. Enterprise, obeying orders from the highest ranks of Starfleet Command, beams aboard a special emissary named K'Ehleyr, a half-human, half-Klingon female. The crew is pulled by Worf's coldness toward K'Ehleyr, who informs them that they must intercept the T'Ong, a Klingon vessel whose staff has been in cryogenic sleep for a century. She reveals that the Klingons began their voyage while the Federation was still at war with the Klingon Empire, and that if they awaken within striking range of key Federation outposts, the results could be devastating. Worf, shunning the emissary's friendly advances, reluctantly follows Picard's orders to meet with K'Ehleyr about the volatile situation with the T'Ong. However, their meeting quickly turns personal, revealing that the two were once linked romantically. After a bitter argument, K'Ehleyr storms out.
A simulated war game suddenly turns into a real-life fight for survival when the crew is ambushed by a Ferengi battleship. As part of the first Starfleet Battle Simulation program, Picard and Riker are tapped to compete against each other in a mock battle. Picard is given command of the U.S.S. Enterprise, while Riker is assigned the Hathaway, a hopelessly unequipped, 80-year-old vessel which he's given 48 hours to outfit for battle. Acting as an observer of the exercise is Kolrami, a master strategist from the Zakdorn race, which is reputed to have the greatest strategic minds in the galaxy. When Riker and his team beam aboard the Hathaway, they are shocked by its dilapidated condition. It quickly becomes obvious that the outclassed ship's only hope for victory lies in outwitting the U.S.S. Enterprise crew. Meanwhile, Dr. Pulaski challenges the arrogant Kolrami to play Data in the highly complex game of Strategema. Although Pulaski is certain that the android's skills will prove superior to the Zakdorn's, Kolrami wins.
During a routine geological survey on Surata IV, Commander Riker's thigh is pierced by a small thorn, which causes him to lose the feeling in his leg. After beaming Riker back aboard the U.S.S. Enterprise, Dr. Pulaski determines that the thorn contains an unknown organism which is rapidly spreading throughout his nervous system. If left unchecked, the microbe will soon reach Riker's brain and kill him. Ironically, Pulaski has no way of decimating the organism without destroying the nerves of the being it's inhabiting. At first, Riker's affliction seems more of a nuisance than a threat. But during a visit with Counselor Troi, his vital signs suddenly plummet and Riker loses consciousness. Although Dr. Pulaski is able to stabilize his condition, she discovers that the organism has spread to Riker's brain. In a desperate attempt to keep his brain functioning, Pulaski begins electronically stimulating his memory.