The Enterprise arrives at Ligon II to acquire a vaccine needed to combat an outbreak of Anchilles fever on Styris IV. The crew, having little information on the Ligonian culture, finds their culture to be similar to that of ancient China following strict customs of status. Specifically, while the men in their culture rule society, the land itself is controlled by the women. Beaming onto the Enterprise with their own transporter technology to provide a sample of the vaccine for inspection, Lutan, the Ligonian leader, is impressed by Tasha Yar's status as a security officer. Yar further demonstrates her combat skills for Lutan on the holodeck. After a tour of the ship, Lutan and his party prepare to depart, but abduct Yar as they transport back to the surface. Captain Picard demands that Lutan return Yar, considering the kidnapping an act of war, but receives no response from the planet. After consultation with his officers, Picard determines that Lutan took Yar in a "counting coup" as a show of heroism. Upon communicating with Lutan in a more peaceful means, Lutan gives the crew permission to beam down to the planet and promises to return Yar after a banquet in his honor.
Lutan announces at the banquet that he will make Yar his "first one", surprising not only the Enterprise crew but also Yareena who believed she was already chosen to be Lutan's "first one". Yareena challenges Yar to a fight to the death to claim back the title of "first one"; Picard objects to the fight, but Lutan refuses to give the Enterprise the rest of the vaccine unless Yar participates. The crew investigates the combat ritual and find that the weapons used are coated with a lethal poison should they make contact; Picard prepares to have Yar beamed to the Enterprise should she be harmed in the battle. As the match progresses, both Yareena and Yar are equally skilled, but Yar eventually lands a strike on Yareena. Yar quickly covers Yareena and orders the transport of both of them to the Enterprise against the demands of Lutan. Aboard the ship, Dr. Crusher finds Yareena moments after death, but is able to counteract the poison and revive her. When Lutan demands to know the fate of Yareena, she reveals that she died, thus ceding the match to Yar and breaking the "first one" bond, but now is able to select a new mate, being Hagon, one of Lutan's bodyguards, and effectively stripping Lutan of his position of power. Hagon lets Yar go and gives the Enterprise their full supply of vaccine.