I like it. Brilliant, whether it is true or not. What about Mystery at Witchend? Can this be decoded. I think so, and this is me and not ODE. Nothing in Mystery is as it seems.
- David the son becomes David the guardian when his father joins the RAF - "Take care of Mummy for me, old chap". You're now in charge, my boy, and look after "those awful twins".
- The family run away from London to Shropshire, but instead of escaping the Germans, they run into them. As soon as they hit Onnybrook station, they meet a violent Jacob.
- They meet Bill Ward, a sailor apparently, who ends the book as a soldier helping the Home Guard.
- Bill Ward warns of spectral dangers, but there are only real dangers. Witchend is to be a place of adventure, not safety, "right by that old rascal mountain". It is the mountain that is evil, not Hitler. Evil is a matter of myth; Hitler is just a man. England is a country of castles and tradition
- Macbeth guards the luggage from the guard who needs to move it.
- Mrs Thurston was expecting a parcel, but didn't get it.
- Witchend is not the end of witchcraft but where the witch, Mrs Thurston, first is encountered.
- 'Peter' is a girl. She although barely a teenager, is mother to her father who is really a child.
- They form a club with an oath, signing on to active service, appointing a captain who they then ignore. Peter, the vice captain, is actually the captain and even beats David in a swimming race.
- They create a hiding place which is not secret, which serves as a fortress with good views, and from which they have to eject an enemy agent who they think is a hero.
- Mrs Thurston is not a nice middle-class lady, but a monster who kicks the dog Mackie. She is not a birdwatcher either, not knowing her peewit from her redshank. She photographed the reservoir and not the wildlife.
- The owl cry was not really from an owl, nor the peewit from a peewit.
- Mr Sterling, rejecting the spy theory, becomes the enemy and not the ally.
- In the world of the wild and the tame, the "awful" twins and Macbeth were the wild, and the spies were (mostly) tame.
- The nice air-force man in uniform is not what he seems either, but a dreadful saboteur. The train he claims to have come on did not exist.
- The twins found others who were not what they seemed and were offered shelter in what was in fact a prison.
- The nice boy with the backpack is wined and dined before blowing up the reservoir.
- Mr Ingles reinvents himself as Home Guard, and sorts out the nonsense before returning to his cows.
- Peter and David are not quite boyfriend and girlfriend. She is far too mature for him.
- The reservoir is not really blown up, as it is quickly repaired.
I was told by the Chief Constable this morning that our countryside is almost certainly harbouring many such unpleasant and dangerous people and it is everyone's duty to do what you children have done and report anything unusual or suspicious. 
David, at the end, has a dream, where an elephant bore remorselessly down like a Juggernaut (both India and Africa were potential problems to the war effort) and on its back Mrs Thurston dressed as a sailor and Home Guard, treachery disguised as friend, or defeated by the sailor/Home Guard Bill Ward. Also, the sea war and invasion, the one protected by sailors, the other by Dad's Army, were both problematic. Her 'white' face showed hatred, European hatred against the colonized. The Nazis were different, they colonised and wiped out white races as well as black and brown. She began singing like a Valkyrie (at which point he woke up, to hear Agnes the 'daily help' singing in the kitchen). The elephant, symbol of the empire, was ridden, even goaded, by its white rider. The empire needs to cure its hatred. The 'commonweal' had to be created. The next generation, the child readers, are tasked to do this.
One last point: in a world of top secrets and counter-espionage, we do not know that any of the adults were telling the truth. Something else for children to get the hang of.