Shy 13-year-old Alex (Evan Whitten) flies from Kansas City to Mexico to meet his extended family for the first time. There, he meets his grandfather and former lucha libre champion Chava (Demián Bichir), energetic, wrestling-obsessed cousin Memo (Nickolas Verdugo), and fearless, hip cousin Luna (Ashley Ciarra). But, just as Alex begins to get his bearings, he discovers a mythical creature living under his grandfather's shed: a young chupacabra cub, which he recognizes from stories of the feared, full-grown chupacabra, fabled to feed on farmers' livestock. Alex soon learns that his new friend Chupa has a secret history with his family, and that dogged, dangerous scientist Richard Quinn (Christian Slater) is hunting the misunderstood creature to try to harness his powers. To protect Chupa from impending danger, Alex sets off on the adventure of a lifetime.