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 Superdog, the Magic Key takes Biff, Chip, Wilf, and Wilma into a comic-style adventure where they meet a small, scruffy dog named Sniff. Despite his appearance, Sniff has dreams of becoming a superhero. When they arrive in a city plagued by a villain called Rayman, who uses a powerful ray gun to cause chaos, the children and Sniff get caught up in the action. At first, Sniff seems clumsy and unhelpful—but when the villain threatens to take over the city, Sniff rises to the occasion. Using his instincts and quick thinking, he helps save the day and becomes the unlikely hero: Superdog. The children cheer him on, and the adventure ends with Sniff being celebrated as the city's new superhero before the Magic Key brings them home.