The Enterprise rescues a Romulan craft pursued into Federation space by a Romulan warbird. The Romulan warbird turns tail and the single Romulan occupying the craft boards the Enterprise, announcing his intentions to defect and claiming knowledge of a secret Romulan installation in the Neutral Zone. At first Picard is suspicious because the defector claims to be an insignificant clerk, but then Picard learns that the defector is actually Admiral Jarok. Jarok eventually gives Picard detailed tactical information, convincing him to investigate the supposed base. The Enterprise does, only to be attacked by cloaked Romulan ships. The Enterprise is ready with three cloaked Birds of Prey, so the Romulans turn tail. Jarok was set up, used as a pawn to lure the Enterprise into a trap. He can never return to his wife and family because he defected, but staying in the Federation will mean that he is tortured if he does not give up Romulan secrets. He chooses to kill himself, and this ends the episode.
And I know that last week I was complaining about that episode being depressing, but here it totally makes sense that Setal would kill himself at the end. Where would he go and what would he do, if he were alive? No doubt he had Romulan secrets that he didn't want to tell the Federation despite his defection, and they probably would have just tortured him until he died any way. Usually I'm totally against stories ending in suicide - don't get me started on how much I hate The Awakening! - but this one I can accept, in part because he isn't a main character of the series. The writers wanted to get him out of the way, and I can understand that as long as his actions aren't out of character, which they aren't. Boohoo, a Romulan died. The end.