May 1837. Ann Blackson, a rich British heiress, is out of place in high society because of her unconventional behaviour. She nonetheless agreed to a marriage of convenience with a cousin. When he inexplicably flees to the United States shortly before their wedding day, she is determined to find him and hastily boards a departing ship. But far from a luxury vessel, The Mermaid turns out to be a rough ship captained by a man with murky intentions.

Unwillingly caught up in a vile trade she disapproves, the young woman finds help in the gruff second mate. She makes him her lover, thinking he is merely satisfying her physical desires, but he will slowly break down the walls she has so carefully built.

Overwhelmed by what is happening on the ship and what is being awoken within her, the very pragmatic Ann risks seeing her life turned upside down by this dramatic journey.