When the Thea Sisters' good friend Bridget has to return to Scotland to help her family repair their ancient castle, the five mice offer to help their friend in whatever way they can. Little do they know that Bridget will be kidnapped, and they'll have to rush to Scotland to help find her! Along the way, the Thea Sisters encounter Celtic legends, cryptic messages, and hidden treasures on a trip that's full of mysteries and surprises!