Data is sent to Barkon IV, a pre-industrial planet, on a routine mission to retrieve some radioactive material from a probe that crashed. Unfortunately, something has gone wrong. Data completely loses his memory and wanders into a village carrying a container full of the radioactive metal. He is soon befriended by Garvin and Gia, a father and his young daughter. Garvin unwittingly opens the container in hopes of finding a clue to Data's identity.
Data is taken to meet Talur, the town healer, who mistakenly deduces that he is one of a race of people rumored to live in the mountains. Gia names him "Jayden," and Garvin takes Data and his metal fragments to Skoran, the town blacksmith. Skoran has no idea what the metal might be, but offers to buy the unique-looking pieces to transform into jewelry. Data sells him half, keeping the rest as clues to his identity.
Unaware that the metal is dangerous, Garvin soon falls ill. As people buy Skoran's jewelry, the mysterious sickness spreads, and Talur, with her primitive knowledge, is unable to find a solution. Sensing that he might be able to solve the problem, Data decides to launch his own investigation, but is interrupted when the frightened townspeople blame him for causing the disease.
Data constructs a primitive lab to study the illness, and Talur offers what tools she has to help him find an explanation. Data searches for a common experience that unites all the sufferers, and stumbles on what could be the answer when Gia falls ill. Noticing that she is wearing a pendant made from his mystery metal, Data realizes that everyone who is sick has had contact with the material, and decides to study it. However, Skoran, who now shows signs of the illness, and two men burst into Data's lab and attack him, tearing away part of the skin from his face. Seeing that Data is made of metal, the horrified men flee.
The men tell Garvin and Gia what they have seen, but once they leave, Data emerges from where he has been hiding and reveals himself to Gia, who still trusts him despite his strange appearance. Having realized the metal is causing the illness, Data continues to work until he has developed a cure, and gives some to Garvin and Gia. He then heads for the town's only well to put the antidote in the water supply, sure that the townspeople will not trust him to cure them. Just as he is pouring in the last of the solution, Data is attacked by Skoran and an angry mob, who apparently kill him. Luckily, however, all of his antidote is deposited into the well.
Later, Beverly and Riker arrive on Barkon IV disguised as townspeople. They meet Gia, who sadly tells them that Data is buried by the well, while the metal that made everyone sick has been deposited in the forest. Data is retrieved and returned to the Enterprise, where he is repaired and reactivated, remembering nothing at all of his experiences.