I read one and a half more of Ross Kay's World War I books. In The Search for the Spy, Earl was very naive and struck me as not being too bright, as he told the spy everything he wanted to know and shipped packages and sent letters for him, without questioning it. I've read half so far of Dodging the North Sea Mines, in which events are highly improbable and Earl still doesn't know much.
Earl, who is in London as the story begins, gets a telegraph from his father saying "Find Leon." Leon is Earl's twin brother, who was in France or possibly Belgium when World War I started. I don't have The Air Scout, which is about what happened to Leon, so I don't know which. Accordingly, Earl sets out to Paris, while just about everyone except British troops are heading the other direction. Perhaps hundreds of thousands -- at least thousands -- of people are fleeing to Britain from the countries on the Western Front where the battles are taking place in August and September 1914.
Fighting in France had events that seemed so much more probable to me. As I said, things like that actually happened. Well, maybe not the part with the airplane, but the descriptions of trench warfare were all too real.