I really enjoyed this adventure for early teenagers. The premise of the book is utterly preposterous, the plot creaks a bit and the language and attitudes are often more 2012 than 1941, but I really didn't mind. It's a great adventure story which carried me along very well.
The plot involves two young teenage refugees from the Nazis living in Britain who agree to return to Germany undercover (after two whole weeks training) to take a child out of captivity and into Switzerland. This mission is vital to the British War Effort at a time when the war was being lost. So far, so unlikely, but it's an exciting adventure not a historical documentary so you need to forget your scepticism and just enjoy the ride. The storytelling is fast-paced and exciting, the lead characters (one male, one female) are engaging, the villain is very villainous and the historical background is well sketched without weighing down the narrative. There are constant narrow escapes and exciting action and I'd have loved this aged 12. I still liked it a lot aged...well...a lot more than 12, and I'm sure it will appeal to young adults of both sexes.
I have one criticism - the map at the front. It is very helpful to know the geography of the area, but it also clearly shows their entire route which acts as a rather large spoiler in places and I'd recommend not looking at it first if you can avoid it. Otherwise it's tremendously enjoyable - perhaps not an enduring classic, but a cracking read nonetheless and warmly recommended.