1869: Emma awakens from a terrifying dream of fire and shadows to find herself in an unknown English town – on the Moon – with no memory of who she is or how she came to be there. Though everyone she meets is unfailingly kind and helpful, no-one can help her with her missing memories, and no-one appears to find their unusual location at all odd.

Joined by James and William, two 'orphans' like herself, Emma sets out to uncover the secrets of her new home, chief among them, who or what is the mysterious Moon King?

Apprenticed to a psychic, and an eccentric fossil-hunting lord, Emma, James and William are separated. But when William goes missing, and everyone around them denies he had ever even been there, Emma and James must reunite to find their missing companion, before their memories of William are also taken from them.

Pursued by the ominous Boatman, their search takes them deep into a system of underground canals and caves beneath the lunar surface, and to a final, terrifying confrontation with the Moon King itself.