Kinley Devereaux and Harper Rowe are agents of the U.S. Government. Laurie Chase is a DEA agent.
The identity of the organization for whom the first two people work is not mentioned here because I have not yet found it in the pages of any of their recorded adventures. It just says they do what they they for the American government. That and what they do is in the "wetwork" category which means that inevitably, someone is going to get very hurt or very dead when they get busy.
The two are close friends who have worked for this mystery department for some time, answering to a woman named Kelly Campbell who had very different feelings for the two. Devereaux she loved dearly and gave him "the cushiest of assignments in the most heavenly of places". Rowe, she hated with a passion and "made it a point to give the worst assignments ... in the hope that, somehow, he would be killed in action."
Laurie Chase, the person who would become the third leg of the team, knows nothing of either gentlemen when she is told to meet up with them in Mexico. She is still shell-shocked from a horrific snafu on her latest assignment with the DEA and had been in the van monitoring her teammates when everything went terribly wrong and they all were killed. Still grieving over them she is ordered to meet up with them. That meeting took place at an airstrip and even before they can say anything, bullets from elsewhere start flying.
That is kind of the way it always seems to go with Devereaux and Rowe. For Chase this is still pretty new but she catches on quickly.
By the way, the source for the very unusual name for the series, picked by the author/publisher, not me, comes from a statement early in the first adventure by Devereaux when he talked of a sniper job in which he "lined up my mark through my scope, and - boom!!...killer."
- After eliminating her target in his hotel room and then making it look like a heart attack, Harper Rowe proclaimed, "I officially un-assassinated my guy".