Meet twins Ali and Tulip. When they're not in lessons, they're solving medical mysteries. Can the twins solve the case of the sweetcorn superstar? A Double Detectives Medical Mystery: The Sweetcorn Superstar is at Oxford Reading Level 8. It is for readers aged 7 to 11 years old who are working below expected standard in their reading. The Readerful Rise series ensures that older struggling readers have books with age-appropriate content and topics, that look like the books their peers are enjoying, but are written at a level they can read successfully.