Gr 6–10— This dual-narrative novel follows siblings Jakob and Lizzie Novis through WWII-era London just prior to the Blitz. Jakob is 19, working as a codebreaker at Bletchley Park, trying to unlock the secrets of the German Enigma machine. His younger sister Lizzie wants to remain in England but is caught in a furious battle with her American grandmother over an attempt to bring her to the U.S. Lizzie is vehement about staying because she wants to locate their mother, an embassy worker who went missing in Poland when the Nazis invaded. And while Jakob doesn't believe their mother is alive, when he and Lizzie start receiving coded messages in the mail, the siblings unite to uncover the truth. This book is an impressive joint effort between Sepetys and Sheinkin. Not only do they present a history of cryptography within details of life at Bletchley Park, they also highlight the Enigma-cracking contributions of well-known figures (e.g., Alan Turing) along with the lesser-known Polish team of Marian Rejewski, Henryk Zygalski, and Jerzy R&3; ycki. Sepetys and Sheinkin have created two protagonists who balance and complement each other in the dual-narrative format: Lizzie is assertive, quick-thinking, and persistent, while Jakob is reserved, thoughtful, and protective. The dangers of life in wartime England are ever present, but this book introduces enough levity to keep the tone light and engaging. VERDICT With broad appeal to both WWII and mystery enthusiasts, this highly recommended title is a first purchase for all libraries serving tweens and teens.— Michael Van Wambeke

Siblings decode familial and wartime secrets in 1940 EnglandHeadstrong 14-year-old Lizzie Novis refuses to believe that her mother, a U.S. embassy clerk who was working in Poland, is dead. After fleeing from her grandmother-who's attempting to bring her back to America-Lizzie locates her 19-year-old brother, Jakob, a Cambridge mathematician who's stationed at the clandestine British intelligence site called Bletchley Park. Hiding from her grandmother's estate steward, Lizzie becomes a messenger at Bletchley Park, ferrying letters across the grounds while Jakob attempts to both break the ciphers generated by the German Enigma machines and help his sister face the reality of their mother's likely fate. With a suspicious MI5 agent inquiring about Mum and clues and codes piling up, the siblings, whose late father was "Polish Jewish British," eventually decipher the truth. Shared narrative duties between the siblings effectively juxtapose the measured Jakob with the spirited Lizzie. Lizzie's directness is repeatedly attributed to her being "half American," which proves tiresome, but Jakob's development from reserved to risk-tolerant provides welcome nuance. The authors introduce and carefully explain a variety of decoding methodologies, inspiring readers to attempt their own. A thoughtful and entertaining historical note identifies the key figures who appear in the book, such as Alan Turing, as well as the real-life bases for the fictional characters. Interspersed photos and images of ephemera help situate the narrative's time period.A rich, enthralling historical mystery that engages and educates.(Historical mystery. 10-14)