Twelve-year-old Gavin Baker, son of a warrior, is a born worrier. With his father serving overseas, Gavin assumes that he's already imagined the worst that can happen-- until he shakes hands with his best friend Javi's long-lost grandfather and finds himself trapped in the old magician's ailing body. Help! As the trickster takes over Gavin's life, fooling the girl of his dreams and even his own family, Gavin wonders if the imposter is a better version of Gavin than Gavin himself. He has to convince Javi that the real Gavin now has hairy knuckles and a love of Pablo Neruda's poetry. Then the boys can try some tricks of their own. But will the two friends be able to reverse the old devil's magic? Or will both of their families get their hearts broken?