"The Defector" is the tenth episode of the third season of the American science fiction television series Star Trek: The Next Generation, and the 58th episode of the series overall.

Set in the 24th century, the series follows the adventures of the Starfleet crew of the Federation starship Enterprise-D. In this episode, a Romulan defector requests asylum aboard the Enterprise after claiming to possess vital information about an imminent Romulan invasion.

Plot

The episode begins with Data exploring the human condition by acting in a production of Shakespeare’s Henry V. Captain Picard is giving Data some constructive criticism when he is notified by Commander Riker that a Romulan scout vessel is being pursued in the Neutral Zone. The scout vessel is under attack by a Romulan warbird, and they are approaching Federation space. The Enterprise moves to intercept the ship, causing the Warbird to cloak and return to Romulan space. The occupant of the ship is brought aboard the Enterprise, and claims he is Sub-Lieutenant Setal, an insignificant logistics clerk seeking to defect to the Federation after coming across information about a secret Romulan installation on the planet Nelvana III, within the Neutral Zone, that could sustain a large Romulan fleet.

Picard and his crew are skeptical of Setal's claims after he refuses to provide evidence, and Picard orders an investigation of Setal's reliability while the Federation relays a Romulan demand for Setal's return to the Enterprise. After Setal's ship auto-destructs, the crew review the records of Setal's arrival, and come to believe that the Romulans have arranged Setal's appearance as part of an elaborate hoax. Picard refuses to enter the Neutral Zone on the baseless claims.

Setal confides to Data that his defection came at a heavy price; he will never see Romulus or his family again. Data attempts to alleviate Setal's feelings by taking him to a holodeck representation of Romulus. Setal dismisses the hologram, then reveals he is Admiral Jarok, a high-ranking officer who led a vicious campaign against several Federation outposts near the Neutral Zone. Jarok again beseeches Picard to investigate Nelvana III, but Picard refuses, and demands Jarok provide information as a test of his conviction. Jarok gives in to Picard's request, and gives detailed tactical information to Picard. Picard orders the Enterprise to Nelvana III.

After they arrive, the crew find the planet barren with no evidence of any installation, to Jarok's surprise. Unexpectedly, two Romulan warbirds de-cloak and fire upon the Enterprise. Picard realizes Jarok was used as a pawn by the Romulans, feeding him disinformation to lure the Federation into the Neutral Zone while disgracing Jarok. In response to Romulan commander Tomalak's demand for the Enterprise's surrender, Picard reveals that he prepared for this: at his command, three Birds-of-Prey, sent by the Klingon Empire at Picard's request (as relayed by Worf), decloak and surround the warbirds, rendering the situation a stalemate. The Romulans re-cloak and retreat, allowing the Enterprise to leave. After the Enterprise departs from the Neutral Zone, the crew discovers that Jarok has committed suicide, leaving behind a note for his family. While Data notes that relations with the Empire make delivery of the letter impossible, Picard states 'as long as there are Romulans with Admiral Jarok's courage and conviction, it may, one day, be possible to deliver Jarok's letter home.