In a cruel orphanage in the seedy town of Blackport, a girl named Harlow lives out her days in fear and toil, longing for the day when her parents will return.

But when a mysterious stranger shows up promising to take her to her father, Harlow unwittingly sets out on a perilous journey to a hidden world to find the truth about who, and what, she is.

A brig full of orphans become her friends. Bloodthirsty pirates wait at every turn. An island of former slaves welcomes her as family. And creatures from her darkest nightmares lurk just below the waves. But something else is stirring in the shadows — a dormant evil is rising once again, and a long lost object of great power may be the only thing that can stop it.