Astronaut Sam Bell's (Sam Rockwell) three-year shift at a lunar mine is finally coming to an end, and he's looking forward to his reunion with his wife (Dominique McElligott) and young daughter. Suddenly, Sam's health takes a drastic turn for the worse. He suffers painful headaches and hallucinations, and almost has a fatal accident. He meets what appears to be a younger version of himself, possibly a clone. With time running out, Sam must solve the mystery before the company crew arrives.