Jonathan Quinn is a freelance "cleaner".
As defined in the series, this is a person who will inspect a clandestine meeting spot to make sure it is safe, or will plant cameras and mikes to ensure a record, or will come along afterwards to remove footprints, tire tracks, and the odd recently-deceased body. They clean up after a mission and strive to make it appear nothing happened.
While he doesn't work from just one outfit, he laments in the first book that he has recently devoted all his time to one small government agency, known only as the Office. Though he begins to branch out, he finds it too easy to call on them for help, making him indebted to them. He is determined to break the dependency.
Just as he was once an apprentice cleaner, taking several years to acquire his skills, he is training a young man named Nate. Nate, who is far too forgiving of Quinn's at-times brusque manners, lost a limb due to an accident which Quinn still blames himself for.
And then there is the beautiful Orlando, a former colleague who truly is the yang to his yin both professionally and personally. She had been the young lover of Quinn's mentor until his death. Years later, Quinn and she reunite and realize the feelings for each other they had suppressed were still strong and needed heeding.
In a released short story, it is revealed that prior to becoming Jonathan Quinn, the man had been a rookie police officer by the name of Jake Oliver but a chance meeting between Oliver and the man who would become his mentor in the business, Durrie, changed that life path completely.
Despite his exceptional eye for detail and an impressive ability to think of his feet, Quinn comes across as an average guy, something he is very pleased with as it makes his movements unnoteworthy and his presence easily forgotten by passer-bys. He stands 5'10 and weigh a light 165.
What makes the series so interesting is that while Quinn gets involved in car chases, fist fights, and gun battles as any agent might, he doesn't want to. He is a cleaner and cleaners don't do that sort of work. He just is darned good at it.