The baby gorilla left in her care grows up to become a hugely tall and broad specimen by the name of Joe, living in the mountains as a mostly unseen legend amongst the people who live there. Along comes eco-minded emissary Gregg O'Hara (Bill Paxton), who is from a California sanctuary, and who talks jungle girl Jill Young (Charlize Theron) into providing a safe haven for Joe at the Los Angeles facility. The transition is not without discomfort, but everything is aggravated via a conspiracy of poachers to get Joe into their own greedy hands.