It is the summer of 1940. The world is at war. Maths whizz Jakob Novis has been recruited to the secret codebreaking centre at Bletchley Park. As Jakob works to crack the Nazi’s Enigma cipher, his younger sister Lizzie is busy on an undercover mission of her own: to find their mother.

This is an action-packed adventure with plenty to keep the reader hooked and seeking to solve the puzzles, missing persons and mysteries all around. It is filled, too, with codes to decipher and explanations of systems to use to keep your communication a secret.

This book is aimed at readers 9-12 but it is a clever and sophisticated read, featuring adult and teenage protagonists, so it's for a mature young reader, I think. A great book. Loved the code-setting.