Jimmie Calvert is an agent with the American Secret Service.
At first I had a question as to whether this Secret Service is a euphemism for American Intelligence or actually means the then division of the Treasury Department. I eventually came to the conclusion that it was in fact the latter and Calvert was an agent with that organization. Interestingly, though, is the fact that though he is proud to carry the badge and to work for the Secret Service, he has chosen to keep his employment as secret as possible so that no one in his statra of society knows he is a government operative.
The first adventure we have of him starts with telling us the nickname he enjoys, "Handsome". Readers will find numerous uses of that name as well as frequent mention of how good looking and dashing he is. In fact, the first page or more of that first story will be devoted to his extremely good looks as well as his background.
Calvert is likely already in his middle age. We are told there were already "a few light touches of silver to his brown hair" which, of course in Calvert's lucky case "did not take from his youthfulness". He was still in impressive shape for his age, not yet having any paunch despite having been "a good trencher all his mature days" [Note: in WW1 slang, a good trencher was someone who made sure he did not miss any meal calls]. Further, "his shoulders were square and his arms and legs gave hint through his rather nifty Oxford gray walking suit of suppleness and strength".
As seems fit for someone of Handsome Jimmie Calvert's stature, women "all liked him". This remained the case even after they learned that while the Calvert name "was written all over the history of Maryland" as his family had once been quite well off, the fortune had long since departed leaving Calvert with "nothing but a family tree". It was this lack of actual money in his bank account, coupled with his enthusiastic love of excitement and danger, that made his working for the Secret Service of such enjoyment.
After Calvert graduated from the University of Virginia likely on a football scholarship where he was a dominating half-back, Calvert needed gainful employment. Trying this and that, all mostly related to sports, he was eventually passed to the State Department. They in turn decided they really had no use for him; "brawn and good nature as exemplified in Handsome Jimmie were inessential". They passed him along to the Secret Service just as the Spanish War started.
Here is where it gets interesting. The intelligence department did not think, apparently, much of him and so sent him off the Spain to spy for them, fully expecting he would end up in a grave over there. He not only survived, he managed to send out valuable intel and to return to the States a year later a seasoned and more than capable operative. Coming back to the States, he continued to be an operative with that governmental agency, albeit as mentioned on the hush-hush.