Cat and her friends are preparing for Halloween night in Clonbridge. While they are planning their routes for trick-or-treating, a troop of fairies and supernatural creatures are also making plans for their annual Revels at Rath Glas, a ringfort outside Clonbridge. These fairy folk enjoy mischief and chaos and have a tendency to steal human children and swap them with fairies or Stocks. As Cat and her granny have the gift of Sight, they're aware that something special is happening in the town this Halloween.

And when two young children disappear, it becomes Cat's responsibility to find the fairies' secret fort and attempt to bargain with the Queen of the Fairies to get the children back - all before dawn breaks.