Emil and the detectives are on holiday by the seaside when they meet the three Byrons. One Byron is the father and the other two are the sons, Mackie and Jackie. Jackie is bigger than Mackie and Byron Senior is very annoyed about it. But what is Jackie to do? When Emil and the detectives discover that the father is planning to desert poor Jackie they are determined to come to the rescue but not before they've been cast away on a desert island.