Jim Chapel is an agent with the DIA.
As the series begins, he is a Captain with the U.S. Army's Intelligence and Security Command and had sat a desk for several years, not by his own choice. Given his choice, he would be back with his buddies and comrades in the Rangers, handling Special Forces assignments in Afghanistan. Unfortunately for him, a Taliban sniper ended that part of his career, as well as destroying his left arm, with one bullet.
A state-of-the-art prostetic that could actually respond to his thoughts replaced his missing limb. It was connected via special wiring to his shoulder and looked quite natural unless examined very closely. It was cold to the touch, though, and was a constant reminder to Chapel of what he had been through.
It also reminded him of what he had endured, especially at the hands of a Marine Top Sargeant whose rehabilitation method was to browbeat his "boys" until they realized that cripples sat on the sideline and wept. His boys were never cripples.
So for the past few years he had worked with Army Intelligence handling cases of fraud, misappropriation, and any other shenanigans that might cross his desk and he was very good at it. He seldom stayed in any one department for more than a few months before changing to another, giving him a wide range of experiences. He found he was a pretty good detective in addition to be a highly skilled warrior. With his arm situation, he expected to finish his career in the military in that field.
Then a strange summons to the Pentagon and a meeting with Admiral Hollingshead of the DIA changed that. The assignment he got then was stranger than anything he could or would have imagined, and it would set him on a totally different career path.
Aiding Chapel in his missions is the incomperable Angel, the nickname given by Chapel to the unseen voice of a female working with the DIA. An admitted teenage hacker who had broken into the Pentagon's secure servers just to see if she could, she was given a chance to stay out of jail by Hollingshead if she went to work for him. When Chapel was first pulled into service, she was assigned to assist and her ability to scour the Internet and sneak into otherwise offlimit servers on his behalf has saved him on several occasions. Their relationship is extremely close since she hears and often sees most of what he does. Nevertheless, she is determined to not complicating their interactions by meeting in person.