Sue O'Connell is an officer with the SOF.
That is the Special Operations Force. It is an elite group of soldiers who are specifically trained to function in highly dangerous and invariably unique situations sometimes in conjunction with other nations' equally skilled forces and sometimes all on their own with little or no backup. They went places common sense might dictate not entering and did things that logic would tell you were impossible. Then they came home to base, rested up a tad, and did it all over again.
O'Connell had been doing so for several years before we are introduced to her in 2000. At that time she and her fellow soldiers were in Nigeria taking on some pretty dangerous folks. For her it is just another very unpleasant, very hazardous mission that would likely never be known about by the general public; and once again she was loving it though she would not likely admit it openly.
But that work is not the reason she is in this compendium of espionage operatives; her membership here comes just a couple years after that flashback. As we are told, "In Afghanistan in 2003, she is severely wounded [said injury taking the lower half of a leg] but decides to remain in the counterterrorism fight by joining 'the family business' of human intelligence collection. Sue lives in the shadow world of special operations intelligence collection hunting both terrorists and the criminal enterprises that support them.
There is no doubt that the series of adventures have this fascinating and extremely capable operative as the lead protagonist; the title for the series, MIKE4, is her callsign within the SOF and she stands centerstage on most of the many missions depicted here. At the same time, however, it is the O'Connell family and not just Sue that could be thought of as the star. Sue comes from a line of operatives who made the CIA, or its precursor the OSS, their life's work.
We will learn about her father, an experienced CIA field agent, and his father, an OSS agent who would be in the founding class at that organization transitioned into the nascent Agency. Both of these men have their own stories well worth telling. But it is Sue who is usually the focal point and when she is not, her extremely interesting CIA agent mother, Barbara, who finds herself deeply involved in very messy problems.
And then there is the fascinating long-running feud the O'Connell family has with a Russian family just as entrenched in their country's Intelligence world.