Bored with sitting pretty on Mermaid Rock, Spirulina leaves her sisters and goes off to find someone else to play with. Whilst having fun with the fishes, she meets Splosh, a baby whale. But Spirulina's new friend has lost his mummy, and when they set out to search for her, all they find is a boatful of nasty fishermen and a large fishing net - just right for catching mermaids...!