A 2362 investigation by an away team from the USS Victory into a vanished colony on Tarchannen III, whose members were unknowingly infected by a parasite that transformed them five years later.
The team was led by Lieutenant Commander Susanna Leijten and included Geordi La Forge. They found the outpost empty, with its forty-nine colonists gone and no explanation, and the case was left open.
In The Next Generation episode Identity Crisis, set in 2367, the former team members begin to desert their posts and steal shuttles to return to the planet. Leijten and La Forge are the last two unaffected. She starts to change aboard the Enterprise-D, and Doctor Crusher removes a parasite that rewrites its host's DNA so that the species can reproduce.
La Forge, who solves the puzzle of an extra shadow in the old survey recording, is transformed into an almost invisible creature and flees to the surface. Leijten coaxes him back in time for treatment. Warning beacons are placed around the planet.