The crew meets children who age backwards.
Tuvok crash-lands on a moon where he finds a group of children from a nearby planet who are under strict orders not to leave the area. He tries to look after them while the crew searches for him, and he learns that the children are not what they seem.
The episode is an unusual look at Tuvok in a caretaker role, and it shows his patience as he deals with the children. It is also built around an unexpected idea about life and aging, and it is one of the most thoughtful stories of the second season, taking a quiet approach to a big question.