The crew responds to a distress call from a stricken Federation freighter that is orbiting the planet Turkana IV, birthplace of their late comrade, Tasha Yar. The freighter explodes, but Data detects an escape pod heading toward the planet. Picard dispatches an Away Team to rescue the crashed crew members. Upon reaching the planet's surface, Riker and his team meet Hayne, leader of the Coalition - one of the planet's two warring factions. When Data reveals that a former crewmember was born on Turkana IV, Hayne offers to aid in the search with the help of one of his comrades, Ishara Yar — Tasha's sister.

Although Picard doesn't completely trust Hayne, he accepts his offer of help, and Ishara is transported aboard the U.S.S. Enterprise. A conference to discuss their options for a rescue is interrupted by a transmission from one of the missing crew members. They are being held hostage by the Alliance, the faction opposing the Coalition, and their lives are in danger. Ishara tells Riker and the crew where the escape pod is being held and volunteers to help. She reveals that as part of a peacekeeping agreement, the members of the Alliance and the Coalition have been implanted with detectors which set off alarms when they cross into their opposing factions' territory. Riker allows Ishara to transport into Alliance territory and act as a diversion. During the mission, she is wounded by the Alliance and is saved by Riker and transported back to the U.S.S. Enterprise.

While she recovers, lshara and Data grow closer. Meanwhile, Geordi determines that the crewmen from the pod are located near Alliance headquarters. lshara tells the crew that she knows the area and could guide them, but her detector implant would alert the Alliance of her presence — and removal of the implant would trigger a micro explosive in the device. Data suggests a way that Dr. Crusher could safely remove the implant and lshara, after considering her options, agrees to the operation. She tells Data that she might like to leave the Coalition and apply to Starfleet Academy after the mission. Picard and Troi question Ishara's motives, but Data urges them to give her a chance.

After the operation, Ishara and the Away Team transport into Alliance territory. After leading the team to the missing crewmen, lshara sneaks away. Noticing that she is missing, Riker and Data set out to find her. Data locates lshara as she attempts to overload the Alliance's defensive systems. She admits that her help on the rescue mission has been a covert attempt to defeat the Alliance. When Data tries to stop her, she fires her phaser at him, barely missing him. Riker diverts Ishara's attention, enabling Data to fire at her. Data then rearms the Alliance defensive systems. Later, Picard returns Ishara to the Coalition, and Riker explains to a disturbed Data that in every trust lies the possibility of betrayal.