Jimmy Christopher, America's top Secret Service operative, returns in THE INVISIBLE EMPIRE, the second novel in this great pulp series from the Thirties. This breathless yarn appeared in the May 1934 issue of the pulp OPERATOR #5. It opens with the maiden voyage of the dirigible Valley Forge being disrupted by the sudden appearance of an invisible menace that knocks airplanes out of the sky or causes them to disappear. At the same time, politicians and military figures begin to vanish into thin air as well, only to be found later miles away, dead from suffocation with their bodies frozen. Leaflets rain from the skies, apparently from nowhere, calling on America to surrender to the might of the Yellow Empire or face annihilation. The only person who can get to the bottom of these mysteries and stop the apocalypse looming over the nation is Jimmy Christopher, Operator 5...that is, if he can stop doing magic tricks for his young pal Tim Donovan and get over his slightly creepy feelings for his twin sister Nan long enough to battle the bad guys.Snark aside, Operator 5 is one of my all-time favorite pulp series. Sure, the stories have their over-the-top elements, and they're not any more politically correct than anything else published in 1934, but they gallop along at a wonderful pace and they're well-written, especially these early entries by Frederick C. Davis writing under the house-name Curtis Steele. A lot of people prefer the later novels by Emile C. Tepperman that center around the Purple Invasion, but I think the first two years' worth of stories from Davis are even better. They have the same crazed apocalyptic feel of Norvell Page's Spider novels, but they're much better plotted and usually have better endings. In reading this one, I thought for a while that I had caught Davis in a plot hole, but sure enough, by the end of the story he had tied everything together in a perfectly logical fashion. In many ways these remind me of modern-day thrillers by authors such as Vince Flynn and Brad Thor, but Jimmy Christopher can deal with worse menaces in a third as many words as those guys' heroes.