Nano has been called back to his home planet due to a number of accidental deaths. Nano's people believe in a planned society. No one in the society is born until there is a need. Nano was born with the specific design to be an explorer and an ambassador in the Federation and Starfleet. It is because of this that Nano has a problem integrating into the Liria culture.
All this established Nano realizes that something more is wrong with his people that is still unrevealed. It turns out that the Liria people are so afraid of the unknown that their fear was manifested by fire and consumed more Liria people then the Enterprise crew were informed. The crew figures this out and Nano is allowed to stay an explorer to help his people adapt to the unknown.