MP-5 is a detachment of agents for the CIA.
This small group of operatives with different areas of expertise work for the CIA but also coordinate with local armed forces in the area of their missions, at least in the first three books where the adventures require close cooperation with the military in first Iraq and then Afghanistan. The designator "MP-5" is occasionally expanded to Marco Polo 5" though no explanation is given.
Leading the group is Rick Gonzalez, a seasoned Special Forces officer who came to the Agency because of his years of experience with "boots on the ground" and was given control of the group. To everyone except his mother, this intelligent and resourceful operative is known as "Gonz".
As the series begins, there are five other members of MP-5 though two have been sent temporarily to Pakistan, leaving three.
Peterson is a very young Army private whose expertise with computers was noticed by Gonz during an earlier mission and who was seconded to MP-5.
"Heisman" is a tall, broad-shouldered African-American who got the nickname because he had almost won the award in college before ruining his knee and his chances for the pros. An expert in Arabic as well as being highly trained in combat, Heisman is someone Gonz is pleased to have around.
McKay is very good looking female doctor who, after finishing her residency, was offered a temporary job with the CIA in exchange for paying off her student loans. As her time of assignment grew to an end, though, she opted to stay with the group for a while longer, seeing what she did there actually making a difference.
Note: The first five novels in the series have been released only in e-book format thus far, though they are available on both the Kindle and the Nook systems.