An emergency call for help from a Federation supply ship sends the U.S.S. Enterprise racing on a course to determine the nature of the crisis.
Upon visually scanning the bridge of the U.S.S. Lantree, the crew is shocked to learn that everyone on the troubled vessel is dead. Dr. Pulaski determines that the crew members, who had been examined and found to be in perfect health eight weeks earlier, have all died of old age. The Lantree is immediately placed under quarantine and the U.S.S. Enterprise heads toward the ship's last port of call, the Darwin Genetic Research Station, to warn them of the potential danger.
Unfortunately, the U.S.S. Enterprise discovers that the residents of the Darwin Station are suffering from the same mysterious affliction. Picard is asked to evacuate the children of the station, who have been engineered to become super-specimens through genetic research. Although the children have been kept in isolation and show no signs of infection, a cautious Picard allows Pulaski to examine just one child until the nature of the virulent disease can be determined.
To further eliminate any danger to the crew, Data and Pulaski board a shuttlecraft and have the boy beamed to that vessel so that he can be evaluated in a safe environment. But moments after Pulaski begins to examine the boy, she is stricken by the mysterious disease, which immediately begins working its rapid aging process on her.
In a desperate attempt to save Pulaski's life, Picard orders the crew to modify the transporter unit so that it can filter out any changes in the doctor by using a sample cell of Pulaski's DNA taken before her exposure to the infection. A short time later, with Picard at the transporter controls, Pulaski is safely beamed back aboard the Enterprise and restored to her normal age.