Alan Beach is a Homicide detective. Jake Riley is a contract agent of the CIA.
They are when we first meet them. They will change a little bit, especially Beach, as the short series progresses but for the most part, that is their lines of work.
Beach is in his late thirties, described further as carrying "a few extra pounds but certainly wasn't fat. Of average height and medium build, he was always dressed in a well-cut, dark suit and tie. His sandy hair was neatly trimmed at the back and sides but the top was slightly tousled. The boyish hair, combined with vaguely rounded cheeks, made him appear younger than his age but his eyes betrayed an inner sadness." As of the first recorded adventure, he has been in Columbus Ohio for three years, moving there from Boston where he was also a homicide investigator until "the Incident" there made him a pariah in that department and necessitated a new home. Eventually, his skills will get the notice of the Bureau and he will move to become a Special Agent with the FBI.
Jake Riley is a former member of Delta Force who was often seconded to the CIA, part of the elite Special Operations Group. Riley was severely injured in a mission to Laos resulting in "deep, jagged scar running vertically from above his right eyebrow to halfway down his cheek". Even worse was the damage to his right knee that require full replacement with a titanium one. Despite those injuries, his "overall physical performance was barely affected". Nevertheless, he chose to retire from Delta and continued "his own private missions, self-funding them with his substantial personal fortune".
The two will each work a situation from their own end until they come together. Each has his own cadre of friends and contacts on which to call but when they do work together, they do so as if they had known each other for years.