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

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.

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.

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

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.

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 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.

After a doctor joins Gus and his crew, they seek a way to the coast and stumble upon a plane owned by a family in desperate need of medical attention.

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.

An unsettling discovery at sea forces Gus to take on a grim chore as tensions swell between his companions. On land, an enemy interrogates Becky.

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.

After a daring rescue, Gus meets an individual well-versed in hybrid history. Amid emotional reunions and eerie revelations, all roads lead to the cave.

With loved ones beside him, Gus goes on a treacherous journey into the cave to find a cure once and for all. Meanwhile, chaos breaks out at the outpost.

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?