"The Secret of Platform 13" is a children's fantasy novel by Eva Ibbotson. The story revolves around a hidden platform at King's Cross Station in London, which leads to a magical island called Brambley. Every nine years, a magical door opens, allowing a group of characters to embark on an adventure to rescue a lost prince. The main characters include a goblin, a giant, and a wizard, who work together to navigate the challenges of the human world. They face various obstacles, including a villainous character, as they strive to bring the prince back to his rightful home.