The school trip to the museum is going badly for David. He is stuck with the class joker, who is getting on his nerves, but then he discovers something terrifying is on the loose. This story is part of the "Oxford Reading Tree: Treetops" series of fiction with built-in progression for pupils aged seven to eleven. Specially written for children who need the support of carefully monitored language levels, the stories are accessible, motivating, and humorous. The series is organized into "Oxford Reading Tree" stages (from Stage 10 to Stage 14), with each stage introducing more complex narrative forms, including flashbacks and changes in viewpoint; descriptive writing; extended reading vocabulary; and more pages, more text, and fewer illustrations. Each stage is supported by a teacher's guide, which offers guidance on using "Treetops" to assess children's reading ability, and includes a variety of activities, many on photocopiable sheets.