Approaching England's North Devon Coast Captain Jesamiah Acorne is worried. A Royal Navy frigate is trailing in his wake and Sea Witch has a cache of contraband aboard. His instinct is to hoist sail and flee, but he cannot attract attention for his wife, Tiola, is ill and getting worse. She says the sea is affecting her, but Jesamiah has never seen seasickness like this before — is it something else? Something to do with her being a white witch?
Like an approaching storm, his worries get deeper, darker, and more sinister. Unpleasant ruffians are looking for a list of traitors' names, Tiola's brother is in jail, and Sir Ailie Doone — the last of the notorious Doones of Exmoor — wants Jesamiah to sail to Cádiz on a secret mission in aid of the Jacobite cause.
Except that being captured by the Spanish and meeting with an old friend, the beautiful English spy, Francesca, is not part of Jesamiah's plan. Once again he is in danger of losing his fidelity, his freedom — and maybe even his life.
Tiola meanwhile has her own fears to face. Why is the ethereal spirit of the sea, Tethys, determined to have Jesamiah for her own? To save him, Tiola must find a way to recall her previous lives and discover why events of the past are influencing those of the present — why the ripples in time are echoing in the ripples in the sand.