Twin sisters, Sophie and Felicity, now have their very own Magic Book! It's their prized possession, gifted to them from The Queen of Serenia (home to the fairies). They start to wonder if there will ever be a cause to use it, when Felicity runs headlong into an underwater adventure, with Sophie close behind. When the girls find themselves out of their depth, an extraordinary rescue by some very unusual new friends leads the girls on to make discoveries way beyond their wildest dreams in a hidden world - just off shore from their favourite beach too! But, peace is shattered in an unforeseen and dramatic turn of events. Tragedy strikes Mermaid City! It seems their only hope is The Magic Book - but how can it help - left high and dry, back up on the beach? Luckily, it has a few surprises left to reveal!