Scientist Richard Quinn is on a quest to capture the chupacabra, a legendary creature, in San Javier to exploit its supposed abilities. While tracking it down in an abandoned mine, he encounters the creature, who, upon being injured by a vehicle, abandons her baby to distract the pursuing scientists. After the passing of his father, Beto, due to cancer, 13-year-old Alex flies to Mexico to connect with his extended family for the first time—a trip that was originally planned for him and his father. In Mexico, he meets his grandfather Chava, a former lucha libre champion, along with his lively cousin Memo, who is obsessed with wrestling, and his brave cousin Luna.
On his first night there, Alex stumbles upon a young chupacabra cub, which starts licking a cut on his hand when he wakes up. Aware of the negative reputation surrounding it's species, Alex decides to keep this a secret. Shortly after, Luna takes him and Memo into town to find Chava, informing them that he often gets lost possibly due to Alzheimer's disease. In the market, Alex sees a colorful figurine labeled "chupacabra," which the vendor surprisingly claims isn't that dangerous.
While retracing their steps home, the kids find Chava walking with a goat that he inexplicably purchased. However, they soon encounter men searching an area for clues, as Quinn begins to collect evidence of the creature's existence. At the ranch, the family watches a news report on the dreaded full-grown chupacabra, rumored to prey on livestock. Chava dismisses the report, deeming it misinformation. Shortly after, Alex confides in Luna that he believes their grandfather is hiding something, revealing a music box he found in the barn. She attributes it to his mental state.
Later, while playing with the music box, Alex hears strange noises and discovers a peculiar creature that resembles a mix between a mammal and a bird, complete with small dog-sized wings. He attempts to feed it sausages from the house and promises to protect it during an incoming thunderstorm. The next morning, Memo searches for Alex and finds him with the friendly young chupacabra, initially causing a panic. However, once Luna arrives, they soon convince her of the creature's gentle nature. Alex argues that they must protect it as if it were a baby, and Chava supports his decision.
Chava reveals a surprising connection, divulging that he accidentally hit its parent with his car and found the baby nearby, opting to keep it hidden from those who would exploit it. However, trouble arrives when Quinn introduces himself, claiming to represent an American government agency on the hunt for rare species for medical research, tracing a license plate from the crash back to Chava. As Chava stands his ground, threatening to demonstrate a lucha libre move to keep Quinn away, Alex promises Chupa that he will find its family.
Memo decides to help Chupa learn to fly, taking it up to the barn roof. After a few attempts that involve some comical crashes into hay, Alex and Chava bond over memories of Alex’s father’s past wrestling career. As Chava reveals that Beto never reached the professional stage due to marrying Alex's mother and moving to America, Alex retreats into his feelings by playing his Game Boy. Chava insists on a playful wrestling match, pushing Alex to confront his emotions. With the knowledge of Chupa's secret ties to their family, and with Quinn hot on their trail, the family embarks on an unforgettable adventure to protect the innocent creature from imminent danger.
