The plot is reminiscent of John Carpenter’s 1981 film Escape from New York which also features a hostage held by a lawless society in a dystopian environment.
Commander Riker (Jonathan Frakes) leads an away team to the surface, where they find the colonists initially unperturbed by their presence, but soon end up in a standoff with one of the colony's two remaining warring factions, the Coalition.
Their leader, Hayne (Don Mirault), reveals that the other faction, the Alliance, holds the Arcos survivors hostage, and offers the Enterprise the Coalition's support in exchange for Federation weapons, a proposal that Riker rejects.
Picard accepts Ishara aboard; although the crew is initially skeptical, DNA tests support her claim, and she gradually gains their trust.
To find the hostages, Chief Engineer Geordi La Forge (LeVar Burton) suggests using the crashed escape pod's instruments; Ishara recommends that she beam separately to a nearby location as a distraction, because her implanted proximity device will set off the Alliance's alarms.
"Legacy" was released in the United States on September 3, 2002, as part of the Star Trek: The Next Generation season four DVD box set.