Alex is a 15-year-old teenager with a secret. Soon after her birth her parents decide to leave Buenos Aires to make a home out of an isolated wooden cabin tucked away in the dunes of the Uruguayan shoreline.

XXY begins with Alex's parents receiving a couple of friends and their 16-year-old son Alvaro from Buenos Aires. Alvaro's father is a plastic surgeon who accepted the invitation because of his medical concern for their friend's daughter. The inevitable attraction between both teenagers forces them all to face their worst fears...

Rumours are spreading around town. Alex gets stared at as if she were a freak. People's fascination with her can become dangerous.