Oona has found a very special egg. She'll do anything to protect this egg until it hatches. Then she can find out what's inside, even though it might just gobble her up! Little brother Thunk, smelly Bruce Brute, and other grimy Cro-Magnony hands in her West Wog world, all want Oona's treasure. More than anything, Oona wants something of her very own to care for.

Now that Oona's dino-baby has hatched from its egg, things have gotten even wackier! Stacy the enormous stegosaurus, can't wait to explore her new world. And Oona can't wait to show her off. But not everyone's ready for this big bundle of joy whose having the time of her life romping and chomping through West Woggle. With Bonk, Bruce Brute, Erma, and even the mean witch, Old Brouhaha, on the case, this loveable babe finds her right place in the hearts of these Stone-Age folks who have come to depend on Stacy Steg to save them from some prehistoric perils.