"Look for the Light," the season 1 finale of The Last of Us , depicts Joel's violent, emotional decision to save Ellie over humanity, sacrificing his morality to protect her. The episode reveals Ellie’s immunity is due to her mother being bitten while pregnant, and concludes with Joel lying to Ellie about the Fireflies' ability to create a cure. Read the full story at Wikipedia . The Last of Us | Season 1 - Episode 9 | RECAP