Charlotte 'Chase' Moreno is an agent with the CIA.
Jonathan Harper is a DEA agent.
I mention Harper here right away because even though Moreno is the main protagonist (IMHO) for these adventures, marked as Agent Provocateur stories, we will spend a good deal of time in the company of Harper so his role nearly warrants his name on the marquee.
But Moreno is the star and what a shining one she is - if someone who looks best in black can be said to shine. She is in her late twenties and the word 'mysterious' used about her definitely seems appropriate. There is a good deal that we do not know about her at first and that is just as she wants it. What we do know, besides her love of the color black, is that she is extremely cool under pressure, quite capable of handling herself in a conversation or hand-to-hand combat, and that she is prone to acting quickly and decisively - or recklessly if you go by some people's opinion; she does not agree and as a reader, neither do I.
Moreno and Harper do not know each other when we first meet them but they will get introduced quickly as they find they are both after the same pair of drug dealers; he to stop a pipeline of cocaine from entering the country and she to stop a large source of terrorist-funding cash from buying deadly weaponry. Since their purposes are different, their methods are different and while where is a definitely physical attraction between the two, professionally there is a different kind of heat.
The two will, no surprise here, become quite in love with each other but watching it happen is what is so entertaining as it is not a smooth ride. Or, as Moreno will tell us at one point down the road, "When we'd first met, we'd gotten along about as well as a rabid raccoon and an Animal Control officer. I wasn't sure which of us was which."