The Oodlethunks are a cave man family. They will remind the reader of the Flintstones in many visual ways, but without the dinosaurs. That is except for the one dinosaur Oona has hatched from a lone egg in Book #1. [ Book #1 is not given a recap, but it does not seem to matter, as this story can stand alone on its own merit.]

Oona’s baby stegosaurus , Stacy Steg Oodlethunk, is eating too much and growing too big to stay in the Oodlethunk’s cave home. Oona’s parents want to set Stacy free, but of course, Oona won’t hear of it.  After school, Oona, her friend Erma, and her younger brother Bonk go to see witch Brouhaha for a magic potion to fix Stacy’s growing problem. Brouhaha says the potion has not been tested yet. It might not work, do not take it. Oona tricks Brouhaha, takes the potion, and gives it to Stacy. The next morning, Stacy is bigger.

At school, the students go on a field trip to Rock Park and the Cave of Echoes. After school, Stacy is even bigger and hungrier.

By the next morning, Stacy has grown so much she is stuck inside the family cave and can’t get out. After school, the students come to see Stacy. Oona has the students collecting food for Stacy along the way to their home in trade for allowing them to see Stacy. Stacy eats it all!  Dad sends everybody home, saying they can come back tomorrow with the entire village to help them get Stacy out of the cave. Meanwhile, the family sleeps outside. The next morning, Stacy is sick and Oona is sick with worry so stays home from school. Once again Oona goes to Brouhaha for help.

After school, the villagers help dismantle the Oodlethunk’s cave freeing Stacy just as the snow begins to fall. Without a cave to stay in the Oodlethunks and villagers go to Rock Park and the Cave of Echoes to wait out the snow storm.  Then, the villagers hears an avalanche has buried their village.  After the snow storm ends everybody goes to help rebuild the village. The Cave of Echoes is big enough for Stacy to stay in all winter.