The book is divided into ten topic-based units or ‘Missions’. The Mission is introduced by one of the Agents each time. 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, where students find the clues to the codebreaking task. There is also a Let’s Revise section at the end of every Mission.