It's the summer holidays and Annie needs someone to play with her. She's fed up at being excluded from the games of her brothers and their friend, Arthur. When Annie discovers that the boys are keeping a secret from her, she's determined to uncover it. After a quick bit of investigation, and a handy hint from Dad, Annie knows the boys are looking for UFOs, and she comes up with a plan to get her own back. Soon the boys have a surprise that's out of this world!