A missing sister, a secret island and ... a sprinkle of sorcery.

The family curse has been lifted and the Widdershins sisters: Betty, Fliss and Charlie are free to leave the misty prison isle of Crowstone. But when a mysterious girl arrives at the Poacher's Pocket with a pocketful of hagstones and accompanied by a will-o'-the-wisp, it seems another adventure has landed on their doorstep. And when Charlie goes missing, it's up to Betty and Fliss to journey through misty marches, past wisp catchers and on to a secret island that doesn't exist on any map...