The Digby and Marvel Detective Agency is desperate for a new mystery to solve, so when Digby discovers a scribbled note saying 'Where is the Promise Tree?, they are determined to help. They meet Lyla-Blue, who has a key she needs to return - but who does it belong to? They might have to delve back in history to find out, and use all of their detective skills, clever ideas and bravery to find the answers. The Digby and Marvel Detective Agency: The Mystery of the Promise Tree is part of the Reading Planet Cosmos range of books from Hodder Education. Cosmos provides a vibrant collection of fiction and non-fiction books that will widen children's reading horizons. Reading Planet books have been carefully levelled to support children in becoming fluent and confident readers. Each book features useful notes and questions to support reading at home and develop comprehension skills. Reading age: 8-9 years.