Leamaneh Castle is rumored to be the most haunted castle in Ireland. Nestled on an unassuming country lane in the Burren, the dark history surrounding its O'Brien mistress is legendary.

In the mid-seventeenth century, Elspeth MacDougall finds herself taken under the wing of noblewoman Mary McManus O'Brien. Or as she is known by the villagers, Máire Rua. Red Mary. Elspeth must try to navigate the politics and dangers of the war with Cromwell's forces, and the threat of Mary discovering just what secrets and abilities her new young companion is hiding.

Cora Murphy is haunted by visions of a young woman who looks as though she could be her sister. She instinctively knows that her brother Colin's problems are related to this mysterious ancestor and the eerie ruins of a castle abandoned for centuries.

Amid these strange occurrences, a person from her past re-enters her life, making her question everything she thought she knew about herself and her abilities.