Heather and stone. A mantle woven in blood. A thread no century can cut.

On the western seaboard of Scotland, where the sea comes and goes around a rocky tidal island, stands Castle Tioram. Beneath it lies the Brat an Dùthchas — the Mantle of Heritage — woven at the command of the Cailleach, the Old Woman of the oldest Highland powers. It was made for sacrifice, not for power, and it passes down a single bloodline.

Each book takes up the thread in a different century. Domhnall mac Somhairle, the bastard son of Somerled, raises the first stronghold and becomes the first Keeper. After Culloden, a broken descendant comes back to the ruins. In Victorian Scotland, an unexpected heir inherits what is left of the castle. And in the present day, a Scottish-American descendant finds that the mantle is waking again.

The Old Woman is there in every age. She is older each time, and she says less each time.