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 traveling companion who suggests a perilous shortcut. Aimee's sanctuary comes under threat. Time's running out for the Singhs.
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.
An uneasy alliance forms over plans to free Gus and the other kids from captivity. Desperate for a breakthrough, Dr. Singh conducts a risky experiment.
Gus' expedition with Dr. Singh leads to several shocking discoveries. Big Man and Aimee seek refuge and reinforcements. Becky connects with a new friend.
General Abbot makes an example out of Gus. Dr. Singh obsesses over his research ahead of an important presentation. Becky crosses paths with a frenemy.
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.