Young Em Smith is brought up by the Waterland family, where she serves as a companion to their daughter, Eliza. But when she finds herself implicated in a horrific crime, she flees for her life. Her frantic escape takes her onto the high seas, where she is at the mercy of the enigmatic smuggler, Captain McDonagh. But there is a more potent force drawing Emily on. There she will confront the astonishing secret of her origins.