Stage 8 in the Oxford Reading Tree series marks an important milestone where children transition from simple texts to more complex narratives. At this level, readers are typically 6–7 years old (Year 3 in UK schooling or equivalent), and are developing fluency, inference skills, and greater reading independence

In The Rainbow Machine, Biff, Chip, and their friends are transported by the Magic Key to a futuristic world where rainbows are artificially made using a special machine. The children visit the Rainbow Factory, where they meet Professor Pong and learn how the rainbows are created and launched into the sky. But when something goes wrong with the machine, the colors get mixed up and chaos follows. The children help fix the problem, restoring the proper color sequence and saving the day. This imaginative story blends science fiction with problem-solving, offering young readers an engaging look at creativity, cooperation, and the science of light and color — all through a magical, accessible lens.