A group of astronauts go on a mission to colonize Mars. After they land on Mars, one of the astronauts discovers she's pregnant. She gives birth to a boy, but dies from complications.
Sixteen years later, her son, Gardner Elliot (Asa Butterfield), is now a teenager who has lived his entire life on Mars, raised by the remaining astronauts. He wants to find his father, whom his mother never named, so he uses the Internet to communicate with Tulsa (Britt Robertson), a teenage girl who lives in Colorado.
When Gardner and the astronauts return to Earth, he begins exploring in order to find his father, but discovers his organs aren't used to the Earth's atmosphere. He's placed in a medical facility but breaks out, finds Tulsa and they go on the run.