Joe Ledger is an agent with the D.M.S.
The Department of Military Sciences is a fairly new organization created because the existing governmental bureaus were not equipped to handle the kind of situations the ever-inventive scientific community makes possible. Well trained operatives from the FBI are fully qualified to handle crime of all sorts. The CIA handles covert activies world-wide. NSA monitors, well, everyone. And the myriad other departments and agencies all have their own niche expertises.
None, however, have had to deal with the sort of problems the D.M.S. fight almost on a daily basis. Things which usually, and thankfully, do not ever make the newcasts. Dangers that often were not possible 100 years ago, or 50 or 20 or, as happens more and more in their line of work, sometimes even last year.
As science evolves ever faster, new potentials constantly come into being and with them new chances for very greedy or very bad people to make the best of them for their own gains. And if a handful, or townful, or countryful of innocents die which some agenda is sought or another billion or two is captured, well, that's progress!
Joe Ledger is one of the front-line operative fighting those nasty sorts, putting his life on the line and barely surviving over and over because as good as he is, the enemies the D.M.S. goes after are just as good at being bad and there are a whole lot more of them than there are of him.
Ledger got his start with the D.M.S. while a detective with the Baltimore police. He was made a part of a multi-jurisdictional task force fighting terrorists on the homeland when an altercation with an al-Qaeda ring changed his life forever. They were smuggling something into the country, something secret but sure to be bad for the nation. When the task force raided their operations, most of them fought back and all of them died. Ledger took care of a few himself.
A few days later he was asked to put handcuffs on a man. This man was one of those he had killed. The man had been really and truly put down. Except through modern science and an especially mad scientist, he got back up again. And he was not in a good mood. Ledger barely survived the reunion and after he permanently ended the man's tirade, he knew he would never be the same.
Leading the D.M.S. was the enigmatic Mr. Church, a man who "invited" Ledger to take on the living dead guy and who would have sadly but quickly done Ledger in should he have been infected. Since Ledger did not die when all indications showed he should have, Mr. Church knew Ledger was the kind of guy needed by the D.M.S. Ledger told him, well, no.
The "no" did not stick. Ledger knew it wouldn't. He hated that it wouldn't. He preferred not knowing that things like the undying terrorist existed. He wanted to go back to tracking down normal killers and bad guys and not have to worry that things a nutso brewed in a test tube not only could wipe everyone out but was planning to do just that. Even worse for Ledger was knowing that it took someone with a killer's instinct and incredibly fast reactive skills to make the correct instantaneous decisions that hopefully will keep the world breathing for another few days. And Ledger was one of those few.
Ledger does not fight the bad guys alone. The D.M.S. has a large assortment of people to battle the bad guys and Ledger gets close to quite a few of them. He saves the lives of many and they return the favor. Some of them do not survive long and all of them know that they are in one of the most dangerous professions there is. They also know that if they do not do the job, a whole lot of other people won't be around long. Perhaps the entire planet.