Cockleshell Cove is a place so boring that the mapmakers didn't even bother to put it on the map. But big adventures can begin in the most unexpected of places...
Penelope Pond loves nothing more than zooming down to the beach in her wheelchair and spending time in her special cave, but everything changes the day she sees someone strange swimming in the sea - a girl, with dreadlocks in her hair and a shimmering tail!
Soon, Penelope is swept into a secret world beneath the waves, but mermaids live by ancient laws where landwalkers are not welcomed. When the rules of both Land and Ocean threaten their friendship, Penelope and Marlie must find the courage to stand up for what's right.