His world shaken, Gus runs off and makes a rash decision. Big Man comes to grips with long-ago mistakes. Aimee makes a last stand against General Abbot.
Gus follows a reluctant Big Man into the unknown. Dr. Singh discovers what it will cost to save Rani. Aimee finds a new beginning after the world ends.
Gus and Big Man pick up a travelling companion, who suggests a perilous shortcut. Aimee's sanctuary comes under threat. Time's running out for the Singhs.
After an eventful, obstacle-strewn journey to find a safe haven, Gus learns more about his origins and how far Birdie was willing to go to protect him.