Scientist Richard Quinn is hunting down the chupacabra, a supposedly mythical creature, in San Javier to harness its alleged powers. Locating one with it baby in an old mine, he chases it. Injured by a passing vehicle, she leaves her baby hidden to lure the pursuing scientists away. Following the death of his father Beto from cancer, 13-year-old Alex flies to Mexico to meet his extended family for the first time, a trip his father had planned for them both. Alex meets his grandfather Chava, a former lucha libre champion, energetic wrestling-obsessed cousin Memo, and fearless hip cousin Luna. Just as Alex begins to get his bearings, on his first night he discovers a young chupacabra cub. He wakes to find it licking a cut on his hand. As Alex realizes they aren't positively regarded, he says nothing. A short time later, Luna drives Memo and Alex into town to search for Chava. She explains that he often wanders off (he may have Alzheimer's disease). In the market Alex sees a miniature colorful figure, which the seller tells him is a chupacabra, which he says is not such a bad creature. Back on the road, the kids find Chava walking with a goat. He bought it but can't explain why. On their return to the ranch, they come across some men carefully searching an area where Quinn finds evidence of what he believes is of the chupacabra. At the ranch house, they watch yet another news report on the feared full-grown chupacabra, fabled to feed on livestock. Chava turns off the TV, saying it's nonsense and lies. Once he goes out, Alex tells Luna that their grandfather is hiding something. He shows her a small music box he found him playing in the barn. She chalks it up to more evidence of his suspected Alzeimer's. Alex plays the music box in the doorway of the barn later. Hearing a mix of cooing and other sounds, he turns to see a strange creature. A mix between a mammal and a bird, furry but with wings the size of a small dog, Alex gets it a plate of sausages from the house to see if it's hungry. When a thunder storm rolls through, he promises to protect it. Alex wakes to Memo looking for him. He tries to usher him out of the barn, but the young chupacabra presents himself as Alex befriended him. He has just gotten Memo calmed down when Luna shows up. Also initially screaming, they show her he's friendly. Luna thinks they should put him out, but Alex insists they need to protect it as if it's a baby. Chava comes in, agreeing with Alex. Chupa, as Alex has named it, approaches him. Chava explains that he'd accidentally hit its parent with his car some nights ago and had found it hiding nearby. He is keeping it a secret as he knows people are looking to exploit it. Returning to the house, Quinn introduces himself, explaining he's from an American government agency which seeks rare species for medical purposes. Finding a license plate from the crash site, he's traced it to him. Chava refuses to let him snoop around, offering to demonstrate a lucha libre move if he doesn't leave. After Alex promises Chupa he will find his family, Memo comes to teach it to fly. Taking it to the barn roof, Memo fearlessly 'flies' into a haystack below. Encouraging it to follow, Chupa gets the wings to work a bit before also falling into the hay. In the house, Chava shows Alex a video of El Perico Verde doing his signature move Suplex, which he had taught him himself. He reveals that Beto was the fighter, but never became professional because he met Alex's mother and moved to the States. Once Chava talks about Beto enough to sadden Alex, he pulls out his Game Boy. He recognizes it's his way of avoiding his feelings. Taking the video console, Chava tells Alex he must fight him for it. Having learned that his new friend Chupa has a secret history with his family and is being hunted by the determined Quinn to try and harness his powers, the family sets off on the adventure of a lifetime to protect Chupa from impending danger.