It is the school holidays and twins Zac and Zoe are forced to spend time with their Grandfather in his rural cottage. They are not happy about this as they would rather be back in London where they have been living for many years. Zac is distracted by his dreams of getting a starring role in an action movie, while Zoe avoids people by playing games on her phone all the time. Suddenly Zac and Zoe are whisked away to a magical and mysterious Purple Sea where they have to use all their action hero and gaming skills to navigate their way through a series of challenges. They meet a motley mix of weird and wonderful dancing sea creatures and find out that Grandpa is more interesting than he lets on.