Jackson Wilder is having a rough time. It's bad enough that he and his dad had to move to a new apartment and leave their old home behind, but Jackson also gets his first loose tooth -- he doesn't want his teeth to fall out! That sounds super scary! With the help of his imaginary friend Irwin the Thylacine, Jackson journeys across deep oceans and rainforest jungles to learn about animals. There's one that loses thousands of teeth, which helps him feel better about losing just one. And when Jackson can't fall asleep in his unfamiliar bedroom, his only hope is that Irwin can introduce him to the best sleepers in the animal kingdom so that Jackson will get good and sleepy, too.