Mark Stone, aka the M.I.A. Hunter, is a freelance agent.
By that I mean he works for no particular agency or corporation. He picks and chooses his clients and his missions and he looks very carefully at both before deciding. Reasonable since his life truly hinges on it.
His official "cover", if that is the right word for it, is that of a private investigator licensed in California. He became one when he got out of the U.S. military after the Vietnam War, needing something to do to earn a living and to make a difference. However, his true vocation is that of person hunting for his fellow soldiers who have gone Missing In Action and who have been, for all intents and purposes, written off by the government. More specifically at first, he was after those actually were P.O.W.'s still held by the Vietnamese. As time goes by, his range increased and his opponents varied. His mission remained the same, though, bringing home those who could not get there alone.
When we first meet Stone, he is around 35 years old having served for most of his adult life in the elite special forces Green Berets, rising to the rank of Master Sergeant. Leaving the service he started up his investigative business but the remembrance of his final days in Vietnam held as a prisoner of war kept him from moving on completely, that and the realization that though he made it back, others did not. Using his own resources, he decided to go back to the jungles to bring out some who were still held there.
Since the government officially were declaring that there were no longer P.O.W.'s, he going after them put him at odds with several different departments, especially the CIA who had its own agendas going on. When he succeeded in bringing back a couple, tensions really added up.
At least for a while. As the series progresses, his expertise in extraction under impossible conditions became too big a calling card for these very same organizations who were having their own people taken prisoner all over the world. If he could bring out the ones from Vietnam like he had, the reasoning went, he could do the same for them. With that his life would change while really staying the same.
Helping Stone throughout his campaigns are three important people.
"Hog" Wiley is a huge man whose looks are bad enough even a good friend like Stone would class him as ugly. In a fight, though, his ferocity and his love of action and mayhem makes him the perfect companion.
Terrence Loughlin is a much more civilized individual. A Brit who served alongside Stone, like Wiley did, in Southeast Asia, Loughlin is the best of friends with Wiley and would willingly give his life to save the other. One would never know it, though, to listen to them.
Carol Jenner is Stone's lady and a lawyer with terrific contacts back in the nation's capital and the chutzpah to use it to help keep Stone and company alive in places they are not supposed to be.