A rip-roaring adventure story of magic, myth and mermaids, featuring Liz Kessler's popular character Emily Windsnap. Neptune and Thor battle for power and their fight upsets the balance of the world. Lightning strikes, curses fly and towering waves swallow a Viking longship and its crew into a watery valley, taking with it the secret of the magical blue crystals. A thousand years later, Emily, a girl who is half human, half mermaid, discovers a bangle with a mysterious and beautiful blue crystal. With the help of her human and mer friends, she discovers the truth about the jewel - and the danger the world faces. The team must race against time to persuade the powerful but notoriously selfish gods of sea and sky to make peace with each other, before disaster strikes.