Philip Mercer is a geologist.
He is, in fact, one of the best mining engineers and consultants in the world and it is that profession that takes him all over the globe. While a considerable number of companies have tried to hire him exclusively, he prefers to pick and choose his clients and assignments, taking the ones that are the most interesting, and charging a hefty fee for his knowledge.
Traveling the world on these jobs, Mercer often finds himself in trouble spots for the simple fact that the greater the chance of riches beneath the earth, the greater the number of people fighting over it. Though Mercer would prefer to avoid such fighting, that invariably proves impossible and he reluctantly finds himself getting involved in more wild and wooly adventures than most spies could dream of.
When he is not traveling, he lives in an old three-story brownstone in Arlington, Virginia, which he had gutted and totally remodeled to fit him. He has a close friend named Harry, nearing 80 in age, who looks after the place when he is away and usually makes himself to Mercer's liquor cabinet while doing so. Despite having made the place just the way he wants it, though, the house is strangely devoid of personal mementos, things he still has in boxes as he has just never taken the time to unpack, even after five years.
Prior to the series starting, Mercer had already come to attention of various Intelligence agencies not only for his reputation as a geologist but also because of an incident just before the first Gulf War when a team of Delta soldiers entered Iraq to find it Hussein was mining uranium. Mercer was asked to go with them as a non-combatant but when the covert expedition was discovered, the leader was killed and chaos followed until Mercer took charge and got those still alive out of the area. This earned him a considerable number of good friends in the Special Forces as well as enhancing his reputation as someone who could handle himself.
The science involved in each of the adventures is deeply involved in the plots of these international thrillers but it is well thought out and simply explained in laymen terms.