A film about identity, genetic inheritance and the family of the future. Donor Unknown follows the story of JoEllen Marsh, 20, as she goes in search of the sperm donor father she only knows as Donor 150. JoEllen has always known her family wasn't like other families. She grew up in Pennsylvania with two mothers, and a burning curiosity to know more about her anonymous donor father. When JoEllen discovers a unique online registry that connects donor-conceived children, she manages to track down a half-sister in New York. The New York Times picks up the story, and, over time, 12 more half-siblings emerge across the USA.