Growing up in a remote cabin with his father, Gus learns lessons about the dangers that lurk beyond the fence to the outside world.

Gus follows Big Man into the unknown; Dr. Singh discovers what it will cost to save Rani; Aimee finds a new beginning after the world ends.

Eager to send Gus on his way, Big Man figures out how to hide him in plain sight; the Singhs attend a neighborhood party that takes an ominous turn.

Gus comes under the protection of some new friends as Big Man's past catches up to him; Dr. Singh fears a neighbor will uncover Rani's secret.

Gus and Big Man pick up a traveling companion who suggests a perilous shortcut; Aimee's sanctuary comes under threat; time is running out for the Singhs.

In a moment of desperation, Dr. Singh makes a bold promise; a lost memento makes for a bumpy ride to Colorado; the Last Men close in on the Preserve.