S5E15 · Power Play

The USS Enterprise detects a distress call at a moon known as Mab-Bu VI. Lt. Commander Data discovers that the USS Essex was lost in the region over 200 years ago. Picard sends Riker, Data and Troi to the surface. Riker injures his arm during the shuttle crash. Transporter Chief Miles O'Brien later is able to beam to the planet's surface with a power booster to enable all four to beam back to the Enterprise. Three orbs of light enter the bodies of Data, Troi, and O'Brien, while a fourth refuses to enter the injured Riker.

After returning to the Enterprise, Data, Troi, and O'Brien take control of the ship and take hostages in Ten Forward. Troi claims that she is Captain Bryce Shumar of the Essex, and Data and O'Brien are her crewmates. She claims their spirits were trapped in the electromagnetic fields of the moon and asks that the Enterprise take their bones back to Earth for burial.

Dr. Crusher determines that the pain receptors in Riker's broken arm repelled the entities possessing the others. La Forge, Crusher, and Ro devise a plan to separate the possessive entities from the crew members' bodies by inducing pain then trapping them in a containment field. However the plan fails when Data suddenly moves out of the attack area. Picard suggests Troi, Data and O'Brien relocate to Cargo Bay Four with hostages.

Troi reveals that the moon is a penal colony, and she, Data and O'Brien are in fact prisoners and not crew of the Essex. They had previously attempted to possess the crew on the Essex to escape the colony, but the ship crashed during the attempt. O'Brien transports hundreds of other prisoner entities to Cargo Bay Four to possess the Enterprise crew and escape, but the bridge crew traps them in a containment field. Picard threatens to blow the cargo bay hatch and kill the prisoner entities (and themselves). Troi, Data and O'Brien relinquish their hosts and Worf beams all the entities back to the moon. The crew recover from the experience.