The Bletchley Riddle by Ruta Sepetys

A thrilling middle grade historical adventure from bestselling authors Ruta Sepetys and Steve SheinkinRemember, you are bound by the official secrets act... It is the summer of 1940. The world is at war. These days, you don’t know who you can trust or who might be a secret spy… 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. Filled with codes to decipher and mysteries to unravel, this is the unputdownable historical adventure that will have you on the edge of your seats.