Two days after Marvin sees a glowing green thing like a flying birthday cake in the night sky, his third-grade class is joined by a mysterious new boy with peculiar behavior.

A small incident during recess threatens to turn nine-year-old Marvin into the outcast of his third-grade class.

After Casey Happleton tells him that if he kisses his elbow he will turn into a girl, nine-year-old Marvin experiments and finds himself very confused about his identity.