Hal Schroeder is a sometime freelance agent.
It is sometime because he has no desire to be an agent any more, not after the crazy things he had to do behind enemy lines during WWII. He wants a normal life doing normal things but life normally finds ways to not let that happen.
The three recorded adventures of Schroeder depict three different groups of American bureaucracy that find need of his services and the dangers they put him into as a result. In none of those cases did he seek out the employment, let alone the danger but that did not stop both from finding him.
Before the War took him away to Europe, Schroeder was expecting to be just an average guy, perhaps a tad smarter than those around him but not enough to get into too much trouble. This intelligence, and the ability to survive in tight situations, brought him to the attention of the OSS once he was in uniform and the powers that be in that organization saw fit to take him out of that uniform, replace his rifle with a ham radio, and parachute him deep behind German lines. There he was asked to report on troop movements, factory activity, key officials' comings and goings, and the occasional bit of sabotage. He did all this to distinction for over two years before the hostilities ceased and he came home.
One trouble with having been a covert operative, though, is when you come home, you are dressed in civvies, looking very much like all the other Joes who never went away and never risked their lives and no matter what you tell people you did, they don't see the uniform so they don't understand the perils and no one bothers to shake your hand or thank you in any way.
And then there is the girl you left behind who you hoped would wait but she didn't and now you have no one and the "heroes" are getting all the action and when you do run across your old flame she is married.
Perhaps that is why when the FBI comes calling with a very strange offer, you start thinking of ways to turn their crazy idea into something that could work for you. And one spot of crazy can lead to another, which is why Wild Bill Donovan thinks you are the man he needs.
Maybe he should have kept his rifle.