Katrina Leonidivna is an agent with the CIA.
She is the field leader of an unofficial group of operatives for the Agency which is known as the Dangerous Clique; described in one blurb in a very misleading "a little-known mischievous unit within the CIA"- misleading because that implies playfulness which does not show just how serious these people can be.
"The story in government law-enforcement circles was that a little after 9/11, somebody high up ... had formed some sort of minimally-supervised team assigned to hunt down up-and-coming minor-league terrorists and take them out before they could advance to the major leagues". This team was nicknamed the 'Dangerous Clique' "because they were close-knit and didn't like working with others".
The offices that the team use in the CIA campus in Tysons Corner is often referred to by both its distractors and its admirers as "the Island of Misfit Toys".
Leonidivna, who is definitely the field leader of the team and deservedly so, is married to her operative partner Alex Flanagan, though how qualified Flanagan is for the field is shown with "Alec didn't belong here, by any measure. He was trained as an analyst specializing in terror financing but had spent years jumping into the field with the ops side, against the better judgment of just about everyone. Katrina's reputation within the Agency was sterling; his ... wasn't. Despite widespread skepticism and more than a few encounters that had gone very wrong very fast, he had managed to keep himself in one piece".
Leonidivna is described as "strikingly and unforgettably good-looking, but hard to place with her exotic Eurasian features and an age that could be anywhere in her thirties to early forties. Katrina was gracious and professional, but [the commentator] could sense that Katrina was used to owning a room - and ... always figuring out how to get out of that room if trouble arrived". One very telling point that helps prove that last is she usually makes sure she wears sensible shoes no matter where; running in high heels doesn't work.
The overall head of the group is Rachel Holtz who "was welcoming but perhaps a bit run down - Raquel seemed to be carrying the weight of twenty-some years of agency work and balancing the strong personalities of her team with changing administrations, changing CIA directors, Byzantine office politics and a world full of troubles. Raquel always seemed close to her wit's end, but that wit's end kept extending a little further each day, because the only thing worse than whatever problems had landed on her desk was the thought of stepping aside and letting someone else handle it".
Two other members of the team are:
Dominca 'Dee' Alves - their NSA-trained teammate and hack-of-all-trades, of whom Raquel says admiringly, "if you tell Dee she can't do something, she takes it as a challenge" and she usually comes through.
Walt Rutledge - described by a non-fan as a 'trigger-happy former Army Ranger', alluding to his Army psyche eval which said he had "an irrational exuberance for using explosives".