Unnatural Selection

Answering a distress call, the Enterprise finds the USS Lantree drifting, its entire crew dead of rapid ageing although they were all young. The only illness on record is a harmless case of flu. The Lantree's last port of call was the Darwin Genetic Research Station on Gagarin IV, where the scientists are now showing the same symptoms. They have been creating genetically engineered children with extraordinary abilities, including immune systems that fight disease before it can take hold. Dr Pulaski suspects the children and insists on examining one herself, but she too begins to age at an alarming rate. The cause is the children's antibodies, which spread through the air and alter the DNA of ordinary people. Using a strand of Pulaski's hair as a template, O'Brien and the transporter restore her original pattern and return her to health. The contaminated Lantree is destroyed to stop the infection spreading.