The circle of power - Sheri Winn

Each of the four Sprite sisters, aged between nine and thirteen, has a magical power related to one of the four elements - earth, water, fire or air. When Ariel discovers her power on her ninth birthday, their circle is complete. The girls' magic must be kept secret, and used only for good; if not, the consequences could be dire.The Sprites' big house in the country is full of laughter and sunshine, but a shadow is falling. Everything the Sprite sisters hold dear will soon be shattered by the arrival of someone who is intent on destroying their power...