When a splinter group of Acamarians called The Gatherers are found to be responsible for an attack on a Federation outpost, the Enterprise travels to Acamar III and attempts to convince planetary leader Marouk to bring the renegade Gatherers home. Marouk is resistant because the Gatherers represent the last vestiges of the clan wars that dominated Acamarian society for centuries, but she agrees to let Picard ferry her and her servants to a Gatherers camp, where Riker and Troi convince the leader Brull to meet with Marouk and hear her proposal. But before negotiations are complete, Marouk's servant Yuta, the last survivor of the Tralesta clan, kills a Gatherer from the Lornack clan. Though his death appears to have been caused by heart failure, Dr. Crusher is suspicious and discovers that a microvirus stopped caused the heart to stop beating. Believing that the old man died of natural causes, Brull forms a tentative alliance with Marouk and tells her that she must meet with Chorgan, the head of all the Gatherers and the only one who can make decisions for the group. During the trip, Marouk encourages a romance between Riker and Yuta, but Riker discovers that Yuta feels more like a slave than a servant and despises her work. During a meeting between Marouk and Chorgan, Riker and Crusher piece together a series of inexplicable deaths in the Lornack clan and discover two things: that Yuta is much older than she appears and has killed Lornack clan members before, and that Chorgan is a member of the Lornack clan. Beaming aboard the Gatherer ship, Riker interrupts the meeting and tells Chorgan that Yuta is a genetically engineered assassin who has come to kill him. Yuta insists that as the last survivor of the Tralesta clan, she is bringing justice, but when she moves to attack Chorgan after repeated warnings, Riker shoots to kill. Acknowledging a debt to Riker, Chorgan agrees to a truce with Marouk.
Analysis: I have absolutely no memory of ever having seen "The Vengeance Factor" before, and I can't figure out whether it's because I actually somehow managed to miss an episode during the original run and subsequent reruns or if there's just so much plot crammed into the episode that my brain didn't bother to retain it. I think I would have remembered a group of renegade aliens with mullets, though. The storyline of this episode is so dense that it really would have been better served as a two-parter, or even a multi-parter like the slow development of the Klingon high command over several seasons, but the Acamarians are never made significant enough to the Federation for the writers to have bothered. The Enterprise stumbles into this mess by being the ship that discovers the looting of an outpost and Picard makes his own decisions about suggesting a reconciliation between the Gatherers and their home planet...very much something Kirk would have done, but pretty close to interfering with another culture's development, since Marouk makes it clear that Acamarian society as a whole has been peaceful since the Gatherers left. It's kind of like expecting the Vulcans to do something about the Romulans because they have common ancestry.
Because so much of the dialogue must be focused on clarifying the historic animosities and current positions of the Acamarians, there's very little room for character development either for the aliens of the week or the series regulars. Thus empathetic Counselor Troi never suspects that anything has gone awry with Yuta, even though Riker can tell just from looking at the girl that she's miserable and hiding her true self. Maybe Troi is too focused on figuring out Marouk, who doesn't seem to be a very bright leader, never guessing that her most trusted servant - her food taster - might have her own reasons for abject obedience. But then, it's Wesley Crusher who gets the Gatherers to listen to reason rather than the trained diplomats on the Enterprise, in a scene that would be sort of cute if nothing like it had ever happened before but instead adds up to one more outrageous score for the boy wonder at the expense of everyone else; wouldn't Picard as captain or Troi as counselor or even Worf as alien-among-humans have been a better choice?
The intensity of the pacing makes the episode watchable, particularly since the audience knows Yuta is a killer while Riker still believes she's a sweet, subservient girl who just needs to be shown a good time. But though actress Lisa Wilcox does a good job portraying Yuta's underlying anger and despair, there's no hint that she's actually decades older than she appears and has been carrying this bitterness for a very long time; I suppose that's how she has managed to get where she is, but it makes it pretty implausible when Riker, Crusher and Data unravel such an enormous secret in just a few minutes. You'd think Marouk would have had some inkling that her very young servant had something odd about her. The scenes between Yuta and Riker seem a bit icky when it looks like she's many years younger than him - it's definitely not an appealing romance, even worse than Riker and Brenna the Hot Irish Lass from "Up the Long Ladder" - and in the end seems contrived only to make Riker feel even worse when he is forced to kill Yuta. I wondered why he didn't just grab the girl and beam back to the Enterprise to take her into custody.
I read a very good science fiction novel by Nancy Kress a few years ago, Oaths and Miracles, about a biotech corporation that can tailor microviruses to trigger heart attacks in specific individuals, and the effects of this research on both scientists who unwittingly become involved and on the small religious cult where the microviruses are tested. Unfortunately, in this episode Yuta is portrayed as a passive carrier; she has no passion for revenge and can't feel pleasure. If she were a fully-formed character, I would wonder whether she took the job as Marouk's cook and taster in the hope of ending her miserable existence as much as to stay close to the Acamarian leader in case of a reconcilation with the renegade Lornacks. Her actions are even more halfhearted than Marouk's suspicious negotiations with the Gatherers, whom she has already labeled parasites and barbarians. If only there had been something to give "The Vengeance Factor" a bit more of an emotional hook for the viewer to go along with the intricate plot.