Captain Jean-Luc Picard and the crew of the U.S.S. Enterprise are veterans of confrontations with the Romulans, but Romulan Commander Sela presents an entirely different situation: She is the product of a rift in time, the daughter of the late Tasha Yar, former security chief of the Enterprise.  The crew encounters Sela in 2368 during a pair of galactic crises: the Klingon civil war, when Sela spearheads a Romulan operation to back the Duras sisters in their attampted coup of the Klingon High Command; and an attempted Romulan invasion of Vulcan.  Sela has the military prowess and strategic cunning of all Romulans, with the added distraction of looking identical to her mother, and therefore presents a double-edged problem for Picard.

Two years before Sela and Picard met, an alternate time line was created when the U.S.S. Enterprise-C emerged out of  a time rift from 20 years in the past.  Yar, still alive in this time line, convinced Picard to send her back with the Enterprise-C to allow her a more meaningful death.  With history restored, the crew (except for Guinan) retained no memories of the time line changes.  Sela tells a desbelieving Picard that Yar was captured in battle with the Romulans.  She was to be executed, but agreed to become the consort of a Romulan general in order to save the lives of her comrades.  Sela was born a year later.  When Sela was four years old, Yar tried to leave with her, but Sela cried out and prevented the escape.  Yar was caught and killed.

Sela provides the Duras clan with equipment and supplies in the Klingon civil war in hopes of eventually fostering war between the Klingons and the Federation if the Duras gain contol of the Klingon High Command.  She matches Picard in battle strategy, evading a trap he sets for her.  But her ships are ultimatley discovered running a Federation blockade, and she abandons her support of the Duras sisters.

Shortly afterward, Picard is sent undercover to the Romulan homeworld to investigate Ambassador Spock's apparent defection to the Romulans.  He finds Spock heading an underground movement to reunify the Vulcan and Romulan people.  Picard teams with Spock to defeat a plot by Sela to invade Bulcan under the guise of a peace envoy.  Sela's fate following the failures of these operations is unknown.