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.

After suffering an unimaginable loss, Gus must make a choice that will determine the fate of humans and hybrids. Who will be left to tell their story?

Gus's quest to find Birdie and uncover more about her connection to his father leaves him questioning everything he's ever known.

Warned about General Abbot's plans, Gus and his friends prepare to take a stand and defend the hybrid kids, no matter what it takes.

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.

The zoo turns into a battle zone when the rescue mission takes flight, with families coming together — and falling apart — during the chaos.

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.

Locked up in the zoo's kennels, Gus meets his fellow hybrid prisoners as he looks for a way out. General Abbot pressures Dr. Singh to produce a cure.

As Gus learns more about a threat and their dangerous plans, the group races to catch a departing boat. Jepperd and Becky face an impossible decision.

Gus and his cohorts set out for Alaska to reconnect with Birdie, who's working on a cure for the Sick. But first, they test their luck at an old casino.

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.

As Big Man reckons with sins of the past, Gus becomes a target of anger and suspicion, Rani's misgivings multiply, and Becky begins basic training.

As polar night looms, Gus and his crew arrive at the outpost — but they're not alone. To find Birdie and the cave, they must brave several obstacles.

Gus' expedition with Dr. Singh leads to several shocking discoveries. Big Man and Aimee seek refuge and reinforcements. Becky connects with a new friend.