Matt Garrett is an agent with the CIA.
More specifically, he is in the paramilitary branch of the Agency which means he goes where the shooting is, usually being the one tasked with doing the shooting. In his early thirties at the start of the series, he has been an operative for several years and has earned a reputation as a man who got the job done, as well as being a man who said what he thought no matter who he was talking to. Garrett is not a hot-head by any means but when truth telling is needed, he is not one to sugarcoat anything.
In this three-book series, Matt Garrett could almost be joined in equal status with his brother Zachary who plays a major role in each of the adventures. While Matt is a CIA agent, Zachary is colonel in the U.S. Special Forces commanding a team of highly skilled soldiers into battle. Matt may be assigned to take out a single target deep in enemy territory. Zachary is called in when more devastating effect is needed.
The two brothers are very close and have been since growing up together in the Charlottesville, Virginia area with their sister Karen. They did everything together, including hunting and fishing and were the best of friends as well as being siblings. When adulthood came and they each went their own way, both chose to serve their country. Matt Garrett's way was similar to his brother but without the uniform.
Much of the action in this series is military in nature and would fall outside the boundaries of the spy world as the books follow Zachary almost as much as Matt. However, the reader quickly sees that it is Matt who is the main star of the series. Zach remains a close second.
Another aspect of the series that make the action so riveting is the duplicity that pervades so much of the actions of the major players who create the situations that the Garretts find themselves in. Some of the actions seem a bit over the top and hard to believe until the reader realizes who the author is and how much experience he has facing the same kind of troubles that Zachary does. It is then that the hard-to-believe becomes a please-tell-me-it's-fiction.