Michael Boutilier is an agent with the IMA. Christina Parker is a student.
Both will change as the 4-book series progresses but that is how they are when we first meet them.
Concerning the organization known as the IMA, the acronym, according to one character, is Integrated Military Affairs. "It's not affiliated with the U.S. military or any other department of the U.S. Government, although they know it exists." It consists of "powerful mercenaries, trained like soldiers".
At first I though the IMA was on the side of the angels but as I learned more, it became less worthy of a halo. Espionage work is certainly one of its activities but eliminations is also a huge part of its income and it does not seem to be too picky who the target is or why. And for those who get in the way, there is an admonition that "the IMA frowned on using hostages for what it called 'recreational purposes' — something that, to this day, remains one of the best euphemisms for [sex] that I've ever heard.
"The IMA had many enemies, with about a thousand different faces." While this line does not really prove anything about the IMA's being good or bad, it does let the reader know that the organization, for being so secret, has a lot of people not liking it.
The teenage Parker comes into contact with the IMA, and thus Boutilier, because of her father who is very much a wanted man and a good way to get to him was through her. As the series progresses, she will age and take on a not-so-helpless aspect, becoming someone you do not want to make angry.
Boutilier will, though he may change employerr, remain a bad-ass. As said early on, "Michael could out-poker-face a slab of stone."