Julie Martinelli is a genius. Joseph Marshall is a Special Forces officer.
In this two-book series, they are two individuals twice who come upon near-Earth ending situations and, by teaming up and working together, use their combination of high IQ and lightning reflexes to overcome impressive odds and save the U.S. if not the world.
Martinelli is a woman in her mid 20's as the series begins and is a graduate student working in a microbiology research facility as a theoretical biochemist while she prepares her doctoral thesis. In the second book, she has her Ph.D but is using her phenominal intellect as a high-level computer programmer and engineer. She has always been a prodigy, having mastered complex machine languages when seven and went on to learn the various forms of mathematics, calculus, and the like on her own. She is also a woman of incredible beauty who exercises and jogs almost religiously to keep her physical form in as peak a condition as her mind continually is.
Marshall is a Major with Special Forces in his mid 30's in the opening book but has gained a promotion to Lt. Colonel by the second. He does not have a genius intelligence like Martinelli but his mind is as sharp as anyone's when it comes to operational matters and his top physical shape and his dedication to not failing keep him a force to not ignore.
Though not partners at the start of either book, and not even knowing each other at first in the opening adventure, they eventually meet and combine their talents to take care of the problem. Along the way they establish a romantic interest in each other though their individual careers make a permanent arrangement somewhat elusive.
Neither of these two are truly agents but for most of the first book and all of the second, they are operative in all by name for the DoD.