Eleven-year-old Jack thought he had outgrown his imaginary friend, George—until his dad also disappears from his life. His mom's bipolar disorder isn’t being properly treated, so while in the throes of a manic episode, she ditches Jack with his aunt, uncle, and cousins. Jack decides that only George can help him figure out where people go when others stop believing in them—and how Jack can put his family back together.

Meanwhile, the imaginary George—half-walrus, half-human, all magic—has a problem of his own: with nobody to believe in him, he is slowly disappearing. Rejoining Jack is his only hope for survival. Or is it?