I must admit to being a little biased, as I loved the previous book,"I Spy"which aso involved Bletchley Park where the top secret decoding work went on. Ned, our hero in this book, is taken away from Bletchley by his Mum, who surprisingly is involved in top secret war work, in a huge cave in Wales. In this remote area accommodation is scarce, so they have to live crowded into a shared house which also houses "aliens" from Europe, who can speak German! So the plot develops and twists and turns. It is cleverly written from the children's point of view, a really sympathetic understanding of their feelings and experiences.