The seventh title in an exciting, magical unicorn adventure series for newly fluent readers, packed full of beautiful illustrations. Zoe and Astra are together again on magical Unicorn Island. And this time they're on an adventure to the Kingdom Under the Sea, where the sea unicorns live, to try and find a precious spell book. They know it's hidden at the bottom of the ocean, in Sea Dragon Cave. They're sure they'll be able to retrieve the spell book, as the dragon isn't real - it's just made of stone... Or is it?