1750s, Georgian England. As a young foundling, Em Smith is brought to Sedge Court, seat of the ambitious Waterlands, to be raised alongside their daughter Eliza. But at the age of fourteen, as her beauty and wit outshine the heiress's, she is made Eliza's lady's maid. And in Eliza's pursuit of a fortune and a husband, Em becomes caught up in a pernicious plot amongst the opulent assemblies of London. When she suddenly finds herself implicated in a horrific crime, she runs for her life. Her frantic escape casts her across the country, on board a ship, and upon the mercy of its enigmatic Captain McDonagh. But there is a more potent force drawing Em on: a spirit whose presence she has felt all her life, and whose irresistible design - be it malicious or benevolent - will force her onwards to a distant shore.