I read this in one greedy gulp today in a library. It was ok, but silly.
It's non-stop espionage action, but as I said silly - the hero is fleeing the police and dastardly wrong-doers who have evil intentions. Never mind why, for God's sake, this isn't the kind of novel in which you wonder why, this is the kind of novel in which you jump on trains going anywhere, and jump off them to run across fields - you only pause to try decipher the coded information in the black note book that you found in your tobacco box - anyway you've hidden that proto-type McGuffin, and you are moving rapidly across a field, you're being pursued by the police so you dodge inside a house. A mysterious man agrees to hide you, but it rapidly emerges that he is the boss of the dastardly evil-doers who are out to get you. Ah, wait a minute, you had no idea that you were going to go here, because you are just running, and jumping, and making split second instant decisions; but either the dastardly evil-doers can foresee your random movements (which admittedly would be both evil and dastardly) or they just happen to have their secret lair in the middle of no-where because it would be an extremely inconvenient location to have their secret lair (which admittedly would also be both evil and dastardly). Anyway, you've been locked up in a back room of the secret lair. Presumably later the dastardly evil-doers will do something either dastardly or evil to you, or possibly even both, which be dastardly, and coming to think of it evil too. You glance around the back room and notice a cupboard built into the wall, you break it open and find a store of explosives and detonators. Obviously years ago you worked as a mining engineer, as we all do, so you rig some up and blow a hole in the wall and escape.
As I said, it's a bit silly. It's also the kind of book in which decent men can size you up and realise by the cut of your jib that you either are good at running and jumping and blowing things up with explosives, or that you are trustworthy, decent, and generally a good egg. This is very convenient because it saves plot time so you can get on with running and jumping, etc, and minimises the page space that has to be spent on bureaucratic verification and other jibber jabber by Jove.
Luckily the dastardly evil-doers turn out to German masters of disguise rather than the Jewish Anarcho-Capitalists who want to assassinate the Prime-Minister of Greece and cause WWI who threaten to be the principal villains in the early pages.
It's not without humour, has been adapted into film, and interestingly is almost entirely without women, one is named who we never meet, while we meet two who are never named. That's right this is an extremely manly book, so manly that breakfast is even cooked by a man. Well obviously so because in the years before WWI in their long dresses and skirts women wouldn't have been able to do all that running and jumping...but on the other hand their long hair pins might have come in handy to combat dastardly evil-doers.