Stage 9 in the Oxford Reading Tree series marks an exciting step forward in children's reading development. At this level, readers are typically 7–8 years old and are beginning to read more confidently, fluently, and independently. Stage 9 books include longer, more detailed narratives, richer vocabulary, and more complex sentence structures, preparing children for chapter books and wider reading.

In Green Island, Biff, Chip, Wilma, and Nadim visit a beautiful island during a holiday trip. But they soon discover that the island's natural beauty is under threat from developers who plan to build roads and hotels, which would harm the environment. While exploring, the children meet a local girl named Leela, who tells them more about the island’s plants, animals, and traditions. Concerned about the damage the development will cause, the children help Leela and other locals come up with a plan to protect the island. They design posters, raise awareness, and speak out against the project. By the end of the story, their efforts help stop the harmful development, and the island is saved. The children learn the importance of standing up for what’s right — especially when it comes to protecting nature.