"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
While Data is performing a scene from Shakespeare’s Henry V under Captain Picard's direction, they are interrupted by a notification that a Romulan scout vessel is fleeing a Romulan warbird through the Neutral Zone, and approaching Federation space. The Enterprise intercepts the ship, and the Warbird retreats. The occupant of the ship claims he is Sub-Lieutenant Setal, a logistics clerk seeking to defect to the Federation after learning 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. After Setal's ship auto-destructs, the crew review the records of his arrival, and suspect 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, and reveals he is Admiral Jarok, a high-ranking officer who led a vicious campaign against several Federation outposts. Jarok again beseeches Picard to investigate Nelvana III, explaining that he has defected to protect his family from a possible war. After persuading Jarok to disclose detailed tactical information about Romulan capabilities, Picard orders the Enterprise to Nelvana III.
When they arrive, the crew find no evidence of any installation, to Jarok's surprise. Unexpectedly, two Romulan warbirds decloak 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. In response to Romulan commander Tomalak's demand for the Enterprise's surrender, Picard reveals that he prepared for this: three Klingon Birds-of-Prey, sent by the Klingon Empire at Picard's request, decloak and surround the warbirds, rendering the situation a stalemate. The Romulans retreat, allowing the Enterprise to leave.
Soon, 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 that as long as there are Romulans with Admiral Jarok's courage and conviction, it may, one day, be possible to deliver Jarok's letter.