Several Miners disappear in a cave. When Mayor Bossabit and some men hear about the disappearance they decide to launch a search party to find the miners. Elderbit tells the Lillibit, Willibit, Snagglebit, and a couple other boys about the legend of the Rainbow Firefly which has been rumored to live in the area of the caves. There is some skepticism from the adults about weather the firefly still exists as it has not been seen for many many years. Inspired by the story Willibit and his friends decide to go in to the caves to search for the firefly. One of the adults tells them to go home, but of course they don't listen. It turns out to be a good thing too because once Lillibit and Willibit split into one party and Snagglebit and his friends split into another party, Snagglebit and his friends discover the firefly. Willibit and Lillibit catch up to Snag and his friends but are attacked by a bunch of bats. Using a torch and some help from Blue the hedge-hog the fight the bats back. After escaping the bats they come to another cave where they find the mayor, his search party, and the missing miners. The children also discover the breeding ground of the Rainbow Firefly. Suddenly some bats come and attack the ground and the children fight them back along with help from the mayor and the other grown-ups in the cave as well. Meanwhile outside the rest of the village has been worried because of so many bits disappearing in the caves. They suddenly see the rainbow firefly fly out of the cave along with the children, the mayor, and the rest of the men who had been in the caves. Everyone in the village is happy that the bits who had been in the cave are ok. As for the rainbow fireflies; they get their own protected sanctuary that the bits of Foothill Forest enjoy for years to come.