The book is divided into ten topic-based units or ‘Missions’. The Mission and the codebreaking task are introduced by one of the Agents each time, and they give students the first clue for the codebreaking task. Then Lesson a, b and c incorporate vocabulary, grammar and skills. Every second Mission has a Lesson d, which provides extra skills practice. Every Mission ends with a Mission Complete page, with a puzzle, a tip or a rap, and the Top Secret Agent Test, where students find the final clue and the solution to the codebreaking task. There is also a Let’s Revise section at the end of every Mission.