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 The Litter Queen, Biff, Chip, and Wilma are taken by the Magic Key to a fantasy world ruled by the strict and unfriendly Litter Queen. The queen has outlawed mess and insists that everything be perfectly clean — but her idea of order is extreme. She punishes anyone who drops even the tiniest bit of litter and controls her land with fear and strict rules. When the children accidentally fall foul of the Litter Queen’s laws, they are taken prisoner. While trying to clean up and avoid punishment, they discover that the queen’s approach has made her people unhappy and anxious. With some clever thinking and teamwork, the children show her there are better ways to encourage cleanliness — like helping people understand why it matters instead of scaring them. By the end of the story, the Litter Queen begins to change her ways, and the children return home having helped make a positive difference.