Catherine 'Kat' Polinski is an agent with the FCA.
That acronym breaks down to the Federal Containment Agency, a little known department embedded in Homeland Security, which is "tasked with investigating foreign diplomats based in the United States". That would sound like it follows said diplomats as they go about their business, keeping track of who they see and what they do, as the KGB was famous for doing in Moscow during the Cold War. The FCA likely does some of that but that is not where they use Polinski.
She has two very impressive talents, as far as the FCA is concerned. The first is she is very good at second-story work, as in breaking into places she should not be in, getting things there (or photographing them), and then getting out again, usually without leaving evidence of her intrusion. The second is her skills as a computer hacker which allows her to sometimes break in without being even on the premises or, if a up-close touch is called for, doing her techie intrusions quickly and quietly.
Polinski currently works for the FCA on five-year 'contract'. "Three years before, on the eve of her 21st birthday, Kat was arrested for illegal Internet hacking. But the government, spotting her talents, offered Kat a deal. For five years, she would work under Bill Cage [at the FCA]. If she stayed the course, she could leave with a clean record. If she backslid or failed to follow orders, she would go to prison."
Regarding those talents mentioned, her abilities at both of those were sharply honed as part of her initial training with the FCA and as such, she is a very valuable asset made even more deadly by the fact that she was also highly skilled in self-defense and in firearms. While she would strive to do her work undetected, should she be discovered, she makes sure that she has a chance to get away.
One other interesting tidbit about this 5'4" slender woman with the short blonde hair. "Every operation Kat does, she copies the stolen information to use as insurance, in case Cage or his superiors ever go against her."