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

A Romulan defector demands asylum aboard the Enterprise with vital information about a possible Romulan invasion.

The episode begins with Data exploring the human condition through acting in a Shakespearean play, 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 war bird, 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 remain skeptical of Setal's claims when he refuses to provide them with any more evidence, and Picard orders an investigation of Setal's reliability while the Federation relays to the Enterprise that the Romulans are seeking Setal's return. When Setal's ship auto-destructs, the crew is forced to review the records of Setal's arrival, and believe that the Romulans arranged Setal 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, that he will never be able to 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 and reveals that he is actually Admiral Jarok, a high-ranking officer who previously had 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 either Jarok provide the full information or he will be damned as a traitor. Jarok gives in to Picard's request, and gives detailed tactical information to Picard. Picard orders the Enterprise to Nelvana III.

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