When twins Amelia and Alexander Fitzpatrick find a mysterious letter from a forgotten relative they're propelled on an adventure that takes them to Ireland where the news that their mum Anya is missing. The revelation that they're descended from the Tuatha Dè Danann leaves them with questions that no one can answer. Charged with restoring the balance between the Seelie and UnSeelie kingdoms they have to locate the Four Treasures before war breaks out.