Joe Hawkins is a visiting professor at Oxford. Kate Farrow is a psychiatrist.
Neither professions sound like the sort that would bring membership into a group devoted to espionage but looks are often deceiving. In this instance, Hawkins is a former operative for the U.S. State Department's highly clandestine intelligence division, working all sorts of missions in all sorts of locales around the world and Farrow is employed in her profession capacity for MI6.
Hawkins is a visiting professor at "Merton College, one of Oxford's oldest colleges", lecturing in such things as "Terrorism, Theory and Policy". He was there under secondment and he had not been there for long. He is said to be somewhat curious as to why he was there; he had been teaching at Columbia back in the States when he applied to a temporary position at Oxford for no real reason other than he "just needed to get out of New York for a while". He had nothing really against New York, even, except that it was too close to D.C. and that city reminded him of the State Department and the job he used to have.
Remembering that kind of work is not something he wants to do but something he will be forced to.
As for Dr. Kate Farrow, when we meet her, she is being reminded by her superior in MI6's psychology department that "National security. That is our top priority. We may wear the uniform of medical doctors, but our first oath is one of allegiance to our country." She is being told this despite her having been with the Firm for three years already. Those many months had been "mainly low-profile casees - monitoring and ongoing interrogation, nothing high risk." as well as occasionally helping MI6 operatives deal with the stress of the job. That is about to change quite a bit as she will be taking part in a severe interrogation of a "senior member of a terrorist network" with intelligence on an imminent threat and that questioning will change her life.
She knows that though she is "still young" but is also "an experienced and highly trained psychiatrist" but if her career with MI6 is going to last, now was the time to not "blow it".
Hawkins and Farrow do not know each other as the first recorded adventure starts but as this trouble envelopes them, they will be forced to become acquainted very quickly and work together or they both will not live to talk about it.