Seb's poor eyesight makes him clumsy and fearful. He can't catch a ball properly and he is scared of swimming in the sea. No wonder he's a disappointment to his sports-loving father. But one summer, when he is staying in a beach house with his father and younger brother, Seb does something extraordinary . . . Seb's adventure starts with a locked cupboard in an upstairs room. What is hidden in there? Where is the key? And what is the strange dolphin out in the bay trying to tell him? As the mystery unfolds, Seb is faced with a frightening task that only he can perform.