The Arcos suffers a warp-core breach and is destroyed, however Lt. Commander Data, the ship's android Chief Operations officer, establishes that an escape pod carried some crewmembers to the planet below. When the Enterprise computer is queried for information concerning Turkana, some grim facts are revealed, including the revelation that fighting among the colonists has destroyed all the surface settlements relegating the survivors to a life underground. A warning is also discovered from the USS Potemkin, the last Federation ship to visit Turkana (six years earlier), which states that the colonists threatened to execute any trespassers.
Nevertheless, Enterprise Captain Jean-Luc Picard sends an away team down to the outpost which quickly makes contact with the Coalition, one of two opposing cadres which control Turkana. Hayne, the leader of the Coalition, tells Enterprise First Officer Commander William Riker that the missing Arcos crewmen have been taken prisoner by the other faction, the Alliance. Hayne adds he will aid in the recovery of the Federation personnel in return for weapons. Hayne is told that a dead member of the Enterprise crew was a Turkana native (although Tasha Yar's name is not mentioned).
Picard rejects Hayneâs offer, but the leader of the Coalition then contacts the Captain and offers the services of Ishara Yar, Tasha Yarâs sister, as a liaison between the Coalition and the Federation. Intrigued, Picard accepts.
Data welcomes the young woman aboard and quickly learns that she does not respect her sister, as she believes Tasha was a coward for abandoning her and leaving her home planet after their parents were killed to go off and join the Federation. Ishara offers to submit to genetic matching to prove her lineage as Yarâs sister and gain the trust of the Enterprise crew. She also provides useful intelligence about the disposition and layout of the Alliance base facilities and is able to give the Federation officers the exact location of the captured escape pod.
The fate of the hostages takes on a new sense of urgency when a communication from the Alliance threatens their execution in 20 hours.
Ishara quickly becomes popular aboard the Enterprise, to the point where Picard sees that in effect she has virtually become a member of his crew. She says she would like to leave the planet and go to Starfleet Academy. Data seems especially taken with her and tells her that although he has no emotions he âbecomes familiarâ with certain people and misses the âinputâ of their presence when absent, adding that this is the case with both herself and her sister.
Using the sensor instruments of the escape pod, Enterprise Chief Engineer Lt. Commander Geordi LaForge is able to locate the hostages and a rescue operation is planned. While LaForge is doing this, Ishara creates a diversion, and Riker leaves the other members of the Enterprise away-team to rescue her.
Isharaâs experience and familiarity with the terrain would prove invaluable to the mission, but like all members of the cadres she was implanted with a proximity detector which sounds an alarm when she enters the territory of the opposing side. This problem is overcome when Data and the shipâs Chief Medical Officer Beverly Crusher design a surgical procedure which allows for the safe removal of the booby trapped device. Ishara gives the small crystalline object to Data, telling him that she wants him to have it. She tells Data she must tell Hayne of her decision to leave, but when she does so she informs Hayne that the plan is "working."
The Enterprise away team is transported into the heart of Alliance territory and quickly achieves the freeing and rescue of the hostages. However Ishara slips away in the confusion.
Following her, Data finds her in the process of setting up an overload in the Alliance fusion generator. When he inquires as to what she is doing, she grimly tells him that the explosion of the generator will disable the Alliance security system, allowing a large waiting force of Coalition solders to overwhelm and defeat the Alliance once and for all. A betrayed Data now realizes that the Coalition has made use of the loyalty and fondness he and the rest of the Enterprise crew harbour toward their missing shipmate Tasha to deceive and manipulate them from the beginning. He attempts to intervene, but Ishara informs him that she is ready to kill him to accomplish her objective. She shoots at him, but misses. Riker arrives and she fires at, but misses, him. Data is able to stun her and disable the overload.
Back aboard the Enterprise, Hayne demands that Ishara be returned, but Riker responds that she attempted to kill two Starfleet officers and the Enterprise is within its rights to keep her. Picard quickly ends the debate by ordering Data to take Ishara to the Transporter room to be beamed down the Turkana. As Ishara is about to be repatriated to her Coalition comrades, she tells Data that if it means anything to him, he was the closest thing to a friend she ever had. The android beams her back to the planet.
Not long after, Data admits to Riker that his thoughts are still with Ishara. Seeing that his Operations officer is still trying to make sense of recent events, Riker comforts him by opining that while some risk is inherent in any act of trust, without it there would be no friendship, therefore those risks are worth taking. Leaving Riker's quarter, Data pauses to caress the crystal proximity detector Ishara gave him.