The Ensigns of Command

The Sheliak, a reclusive species bound to the Federation by a long and complex treaty, demand that every human leave Tau Cygni V within three days, or be wiped out. The planet is theirs under the treaty, but a human colony has been living there for generations. Radiation blocks the transporters, so Data goes down by shuttle to organise an evacuation. Colony leader Gosheven refuses to leave, and Data's logic carries little weight with people proud of what they have built. Helped by the young engineer Ard'rian McKenzie, who grows fond of him, Data finally makes his point by destroying the colony's aqueduct with a modified phaser, proving how helpless they would be against an attack. Gosheven gives way. Meanwhile Picard combs the treaty and invokes a clause demanding third-party arbitration, which forces the Sheliak to allow the colonists enough time to leave safely.