Cuthbert Croom is an agent with the British Diplomatic Service.
I state upfront that I have not gotten a chance to read any of the stories in the collection of adventures of this operative, the cost of the two copies I had found being too high right now. The following are excerpts from books about the series by others, as noted.
In David Stafford's excellent The Silent Game: The Real World of Imaginary Spies from 1985, Croom was described as "a Wykehamist [graduate of Winchester College] whose bookish personal inclinations are constantly frustrated by his patriotic duty, which demands he mingle with the meretricious glitteraty in order to pull the country back from the brink of danger". [Note the intended definition of 'meretricious' being 'apparently attractive but have in reality no value or integrity.]
In the trade publication Canadian Bookseller and Stationers' Journal, volume 18 from 1905, the reviewer stated "if Cuthbert Croom, secret agent in His Majesty's Diplomatic Service, had been less of a ladies' man he would have been a far more successful agent. Mr. Croom was supposed to be a clever unraveller of mysteries, yet in the fifteen stories that make up this book, Cuthbert Croom confesses how he was caught again and again in a net spread in sight of the bird. He never went abroad but mysterious ladies attracted his attention, turned appealing eyes towards him, and were induced to pour their tales of woe into his sympathetic ears. The ladies, in an exceptional number of cases, turned out to be princesses, or at least they said they were, which is not always the same thing. On various occasions Mr. Croom found himself cast into dungeons and cellars and murderous weapons descended upon him, moved by mysterious mechanical contrivances. We read in several stories how different ladies were each the one love of Cuthbert Croom's life."