Finn has always been different and in the tiny Scottish fishing village of Stromhead, he sticks out like a sore thumb. One day he dives into the sea and finds that, swimming with the dolphins, feels completely like home. But his new friends are in danger of being injured by the rubbish that floats out into the water and now a supermarket is going to release thousands of balloons that could drift out to sea and cause even more damage. Desperate to help the dolphins, Finn goes to the Lighthouse Crew, a group of kids who have always left Finn out. Will they be able to set aside their differences to save the dolphins? And what will Finn discover about his past along the way?