The Counter-Clock Incident

While en route to Babel transporting Commodore Robert April, the U.S.S. Enterprise's first captain, and Dr. Sarah April, his wife and ship's first doctor, the Enterprise inadvertently locks a tractor beam on a ship diving into the Beta Niobe Nova. Both ships plunge through the nova and into a bizarre parallel universe where everything is backward. With time flying in reverse, the crew begins to grow younger at an accelerated rate.

Synopsis adapted from TVmaze (CC BY-SA 4.0)