Buddy, an adopted T. rex, wishes he knew more about his T. rex ancestors. So, Dad takes him and Tiny on the Dinosaur Train back to the early Cretaceous, to visit an ancestor: an earlier version of Tyrannosaurus rex called Raptorex. Rodney Raptorex is a kid who won't grow up to be as big as Buddy will, but the two boys find that they not only have a lot of differences, they have a lot in common, too. The kids are stuck cooped up in the nest for a long, rainy spell which leads to them fighting. Mom tells them that the rain has stopped enough that they can leave the nest but she gives them an assignment: to go find their own "calm space," where they can calm down enough to get along with each other again. It works - each kid finds something in nature that helps him or her to calm down and be friends again.