Dr. Leonard "Bones" McCoy meets a former girlfriend when the Enterprise brings supplies to a remote archaeological survey group. Still attractive to McCoy, the woman's current appearance and her colleague hide a deadly secret, ultimately revealed as a tragedy of ecology.
After attacking an outpost, Romulans battle the Enterprise.
An alien virus picked up from the now-dead Psi 2000 outpost strips the crew of their inhibitions, causing chaos as each individual is overcome by hidden emotions -- even Spock. Meanwhile, the disabled crew have left the Enterprise unable to react to the planet break-up below that is pulling them down.
Raised from infancy by noncorporeal beings, 17-year-old Charles Evans is ferried by an Enterprise crew unaware of his true nature. Once aboard, the teenager develops a crush on Yeoman Rand and proves dangerously unable to wield his enormous psionic powers with maturity until higher authorities intervene.
After falling ill to what appears to be a repressed memory Tuvok must perform a mind-meld with Captain Janeway in order to survive. The meld takes them back to when Tuvok was a junior science officer aboard the USS Excelsior under the command of Captain Hikaru Sulu.