After the events of Halloween, Cat and Shane are once again fast friends, but they're about to learn that the turning of the seasons brings new challenges to deal with...
When new neighbours move into the estate - Dr. Becca Ryan, a pink-haired witch who's researching holy wells in the area and her familiar Vinnie the stoat - Cat and Shane quickly befriend them. Little do they know Becca's research has disturbed the very old and very dangerous spirit of Cethlenn, a Fomorian queen who is determined to use Becca and the children to exact her revenge on her ancient enemies, the Tuatha De Dannan by taking over the land that was once theirs.
Cat and Shane are both dealing with difficulties at home, so when the spirit of Cethlenn possesses Becca and tells Cat of an ancient artifact that once belonged to The Dagda himself - a harp that, when played, could influence the mood of anyone who hears it - she and Shane become convinced that the harp is the answer to their woes.
On their adventure, Cat and Shane learn many things about themselves and their motivations. They come to realise that their problems cannot be fixed by magic and resolve never to use the harp.
Can they free Becca from Cethlenn's clutches and destroy the harp before Cethlenn uses it to summon an army of dead Fomorians to take over the land?