Hope is an anchor, and Natalie Morrigan is drowning.

Haunted by a power she can't control, Natalie and her friends are determined to reunite their families and uncover the truth of their past. But with Leo missing in action and Uncle Chris out of the picture, Natalie is left harboring a mysterious key and a secret that isn't hers to tell.

Invited to masquerade as a Nautilus recruit, Natalie finds herself in the Helix: Nautilus's center. Faced with old enemies and locked doors, she hopes to last long enough to find her parents.

But Natalie isn't the only one keeping secrets.

With the fate of the world and her powers at stake, Natalie soon realizes the most dangerous demons she must conquer are her own.

Lest they drown her first.