Ten-year-old Pax Jackson doesn't know if he'll make it to his next birthday. He has cancer. And he's about to embark upon an unforgettable adventure. At their favorite climbing tree, Pax and his best friend, Jayni, meet Wilmer—a comical bellbird who introduces them to a magical realm of delightful and bewitching creatures.

The children sail a vast sea, navigate a frightening forest, and summit a perilous mountain in search of a mysterious man who might be able to heal Pax. Will they be thwarted by a malevolent weeping willow, a horde of Bumfuzzles, or the dragon snake? The kids face their fears and the lurking evil that threatens to destroy them. And they also contend with their own inner struggles: Pax, wounded by Jayni's ignorance of suffering, and Jayni, resentful of how Pax's illness has changed him.