Cal Dexter is a former Tunnel Rat.
In truth, he is a former many things but his first major claim to any significance was as a Tunnel Rat during the Vietnam War. It was in this 'police action' that he was picked due to his apparent fearlessness to infiltrate the hundreds of tunnels the Viet Cong dug throughout that war-torn region to move men and supplies without being spotted. To fight an enemy such as this, it was necessary to go in after them but considering the incredible dangers from ambush, horrific death traps, natural cave-ins, and creatures that only come out in the dark, it was a fight that very few were capable of waging. He was one such person and he was one of the very best for more months than anyone should have had to endure.
But his gallantry and bravery during an impossible assignment is not why he is mentioned here. That comes much later. For Dexter what came after the War was college on the G.I. Bill and then a law degree. A wife and a much loved daughter followed. His life was pretty good. It stayed good for 16 years. That is when his teenage daughter met and fell hard for a Latino man who promised everything and took her away. What he took her to was a life of forced prostitution and eventual murder. The lover had fled to Panama and was fighting extradition. Dexter used the skills he had learned so many years before and tracked the hated man on his own turf. Those who killed his girl died. But tragedy did not stop there. Returning home, he discovered that his wife, anguished at their daughter's death, had taken her own life. His wonderful world was destroyed.
Needing something to grab onto, something to give his shattered life some reason for continuing, Dexter moved to a small town far from his former stomping grounds and set up a law practice that seemed to have little action. In reality he had started a service for people who had been like him, victimized by perpetrators who could flee to another country and laugh at the law. He chose not to kill them. That he had found with his own daughter's killer was too easy on them. He found ways to bring them back to the States to stand trial. He took the codename of Avenger for those needing to use his services.
The Dexter story is really two parts.
The first part is an adventure he has in his capacity of Avenger, hunting down the killer of an aid worker in the ravaged area of former Yugoslavia. What makes this tale of vigilante law enforcement and rendition at all spy related is that unbeknownst to him as he hunted the Serb killer, that man was promising to use his contacts to arrange a meeting between a senior CIA operative and pre-9/11 Osama Bin Laden.
The operative was Paul Deveraux and he was hoping to capture the Saudi terrorist for his previous crimes but had found the target far too wily to catch easily so subtefuge was needed. The Serb was a conduit and Devereaux needed him alive and unmolested for a month. Learning of the Avenger's interest, it became a conflict detailed in the first book.
The second part takes place quite a few years later. Dexter was in his late 50s at least and had several years before stopped his extracurricular activities. He was just getting too old for it. Paul Devereaux had himself retired soon after the previous adventure. He was done with the spy game though he knew in his heart that he missed it. When the President called with an extraordinary request, Devereaux could not resist the challenge. The assignment was to, totally off the books but extremely well funded, find a way to break the back of the cocaine industry.
While Devereaux knew, even if the President and his advisors refused to see, that nothing could stop the sale of the drug as long as the demand was as powerful as it was and the profits so obscenely huge, he did think there was a way to deal such a major blow to infrastructure that it would be crippled for years and no one cartel would in control as existed then. It was a daring plan and he needed someone extremely smart, crafty, brave, and gutsy to be his field operative.
Though there were many he knew in the Agency, the name he thought of first as being the best man for the job was a middle-aged lawyer from the sticks, a man he had never met in person but who was the only man to have ever beaten him.
He called on Dexter.