Books in the Witches of Orkney series

Orkney is on the brink of war now that the witches have destroyed Odin's Stone-the powerful talisman that kept the balance. With the evil he-witch Vertulious returned to his full form (thanks to Abigail's help), nothing will stop the witches from taking over Orkney-unless Abigail and Hugo can find a way to balance the power. Can Mjolnir, the hammer of Thor, do the trick?