Joe is a spy-in-training.
Joe is all we know him by. If there is a last name given, I could not find it. We see lots of references to Joe, of course since he is the star of the adventures. There are a reasonable number of Mom and Dad references and a good deal of comments about Sam (more on her in a moment) but last names are not given. They are given for some of the people that Joe runs across but that is normal because kids Joe's age must always be polite and use Miss or Mrs. or Mr. as appropriate.
Now on to the spy-in-training. This is the part that Joe is so very excited about because all his life (okay, being as how he is apparently around 8 years old, that's not all that many years) he has been a huge, huge, big time, major fan of spy books. At least I guess so because the only series he talks about is about 'Dan McGuire'. He loves the Dan McGuire series of what sounds like awesome spy books. They have great names like 'Dan McGuire and the Six-Legged Invasion' and 'Dan McGuire and the Case of the Chipped China'. Joe has learned a lot about being a spy just from reading those stories and I think he has read everyone several times.
But back to the training part. How did a young kid get to be in training for how to be a spy?
His parents are spies. He did not know that when we meet him in the first recorded adventure. Mom and Dad were, well, just Mom and Dad. Except it turns out they were also spies. And their covers were blown. Someone told someone else something and now really bad people are out looking for them. Be on the lookout for a woman who looks like Mom and a man who looks like Dad. Oh, and they have a young son named Joe so look for him, too.
So to protect themselves, they packed up and moved to a new town. They took new identities (still don't know any last name!) and wore disguises all the time too but there was still the matter of the boy who looked like Joe. That's when they came up with the horrible, terrible, don't-even-think-it idea that they could disguise Joe as ... Josie. Yep. Mom decides the best way to hide 'him' is as a 'her'.
Mom and Dad know the truth, naturally, as does Joe. And so does Sam who is the girl Joe's age in the neighborhood they move to because she figured it out and since then she had been getting the same spy training that Joe does because, well, she wants it and she knows the truth and all. And when there are these training sessions and occasionally a real actual no-kidding mission, she gets to take part, too. Which is good because she is all sorts of good with athletics which Joe isn't so much.
And she is really used to wearing girl stuff which Joe is not either. And a whole lot of the three adventures of Joe, one of the spies in disguise, is about dressing up like a girl. Yuch!