Geoffrey Callaghan is the head of British Military Intelligence.
Being in the Army himself, Callaghan holds the rank of Colonel as he leads what amounts to the total of intelligence gathering for the British Empire before the turn of the 20th century. His career there must have been quite interesting because he has from the time we first meet him the nickname of "Steel". Why is as yet unknown to us but definitely leads the reader to believe that either his pre-Intelligence military career was challenging or his time in charge of all military intelligence gathering for the Crown needed tremendous fortitude. Or both.
Callaghan's area of operations is worldwide because the British Empire still maintains considerable control across the globe. We can watch him first work diligently with his select team as well as operative from French Intelligence to interrupt rampant arms sales to the Far East, providing counter-forces with the means to contradict laws and edicts from the U.K.
In his next recorded adventure he and his closest assistant, a man named Yusuf, travel to the Northwest Frontier of India, in a region that would later become the country of Pakistan. It is there that a group referred to as "Haji" are becoming extremely active in disrupting British control of the area and it falls to Callaghan and company to find out who these mysterious rebels are, learn where they are headquartered, and determined how best to put down the revolt.
The third adventure sees the intrepid Colonel, along with a good friend, in South America helping out a woman to fight off a band of very persistent and dangerous raiders who want the priceless Inca jewel she has - but the question then arises of where she got it in the first place!
Callaghan may be the head of an Intelligence branch but he definitely sounds like a hands on person. In the blurb for the third tale, it is said "he was not the man to await his chance; he created opportunity by carrying the war into the enemy's own camp. 'Act first and ask afterwards' was a slogan that had always served him well in the past and there seemed no reason why it should fail him now. and when Callaghan moved, things began to hum."