The Tweenies are singing and fishing. Everyone has managed to land a fish, except for Jake. They discover that someone who is half fish and half person is called a mermaid. Fizz and Bella get very excited about this and decide that they should become mermaids. They find what they need in the dressing up box and together with Milo and Jake they explore and sing about these wondrous creatures. Mermaids may not be real but they're fun.