"The Defector" was written by Ronald Moore and was the 10th episode of the 3rd season.
A Romulan ship is in hot pursuit of a rogue scout ship manned by a lone Romulan heading out of the neutral zone and into federation space. The scout is heavily damaged and the occupant is injured and after the pursuit ends at the front of federation space, the Romulan is beamed aboard.
He claims to be a lowly logistics clerk, but reveals later he is a Romulan admiral named Jarok who once lead a fleet in a battle with the federation. He says the Romulan Empire is planning another war with the federation and gives them information he was given when reassigned to a remote outpost. He relays this information and confides in Captain Picard that he is doing this to preserve his children's future and to save the Empire which otherwise may not survive another war.
The planet to which Jarok tells the crew is the homebase of the Empire's strategic base is actually a dead rock with no lifesigns or tactical base. Picard and Jarok come to realize it was a ruse to test Jarok's loyalty by the Empire. Romulan ships decloak and demand the Enterprise surrender for violating the neutral zone treaty and acting with military aggression. Then three Klingon vessels appear decloaked, ready to do battle with the Romulans. They were summoned to the same destination by Worf as a means of protection and giving the federation a tactical advantage.
The Romulans back off and head back to their territory. Meanwhile, Jarok is back in his quarters. He commits suicide but leaves behind a letter to his family in hopes that one day it will be delivered to them.
This episode was exciting from the beginning and was well-acted and written. Along with the Enterprise crew, we too are in doubt of Jarok's sincerity until that moment on the bridge when confronted by the dead planet and the Romulan ships. Many good points were made about war, including the need to preserve, through peace, a future for our children. As Jarok tells Picard, his daughter may grow up to view her father as a traitor, but at least she will grow up.
There is also funny dialogue where Geordi explains to Data what he meant by "catching the Romulans with their pants down."