At the close of last season, Worf resigned his Starfleet commission to join the Klingon Council army as civil war divided his people. Despite his sympathy for Worf, Picard refused to involve the U.S.S. Enterprise in the internal Klingon struggle. Yet fearing that the Romulans are secretly supporting the subversive Duras family in hopes of destroying the Klingon alliance with the Federation, Picard convinces the head of Starfleet to initiate a blockade against the Romulan Empire. He immediately assigns his crew members to posts on Starfleet ships and dispatches the fleet to the Romulan-Klingon border, where they hope to prevent the flow of supplies and equipment from the Romulans to the Duras family.

As dissension spreads in the Klingon Home World, Worf is kidnapped by unknown Klingon assailants. Meanwhile, the Duras sisters, Lursa and B'Etor, continue to meet with a mysterious woman, a Romulan commander named Sela who bears more than a slight resemblance to the late Starfleet officer Tasha Yar. The group discusses their plans to gain control of the Empire, but are upset to learn of the pending intervention of the Federation fleet.

Hoping to convince Picard to disengage in the war, Sela pays a surprise visit to the captain. Picard is shocked when Sela claims to be the daughter of Tasha Yar, but Guinan later convinces him that the young woman's claims may be true. Guinan insists that she somehow remembers Picard sending Tasha to a previous U.S.S. Enterprise 23 years earlier from the future. Because of this, Guinan points out, Picard is indirectly responsible for Sela's conception.

Picard calls for a meeting with Sela, who presses him for information about Starfleet strategy and gives him a fourteen-hour deadline to either retreat or prepare to be attacked by Romulan forces. Picard reveals nothing and instead focuses the questioning on her heritage. When Sela corroborates Guinan's story, Picard realizes that the young woman is really Tasha's daughter. Meanwhile, Worf's kidnappers deliver him to the sisters of Duras, who try to convince the Klingon to join their side of the battle by marrying one of them. Worf, naturally, refuses the offer.

With time running out, Picard decides the only way to avoid all-out war with the Romulans is to expose their involvement in the Klingon civil war. He convinces Gowron to launch a massive attack, causing the sisters of Duras to call for supplies from the Romulans, which in turn forces the Romulans to run the blockade. When the Romulans are discovered, Sela orders them to turn back, leaving the sisters of Duras without help. The subversives accept defeat, and Gowron is reinstated as leader of the High Council, while an injured Worf escapes his captors and returns to duty aboard the U.S.S. Enterprise.