While visiting Data's home planet, the away team discovers a laboratory containing android body parts. When Dr. Crusher and Chief Engineer Argyle assemble the parts, they bring to life a duplicate of Data! The real Data learns that the look-alike, named Lore, was once "alive," but was disassembled by the colonists on the planet who were jealous of Lore's perfection. As a result, a less-than-perfect android, Data, was constructed.
Unbeknownst to the crew, Lore gained revenge on the planet's inhabitants before being disassembled. He unleashed a ravenous crystal entity onto the colonists — an entity which feasts on intelligent life forms — thereby erasing all life on the planet.
As part of his scheme to turn the entity loose on the Enterprise, Lore renders Data unconscious and impersonates him. Just when he's about to succeed in his plan, Wesley Crusher recognizes Lore and urges his mother to find Data. Once back on his feet, Data beams Lore into space during a spectacular android skirmish.