Anna Martin is an agent with MI-5.
Adam Levy is ... not. Exactly who Adam works for as the civilian he is does not get mentioned. He works for some commercial enterprise where he teaches "people how to use software programs" and "how to prevent anyone from hacking their files".
Apparently that job takes him out of his home office a fair amount for it was while returning from doing it that Adam happened to be in a stall in the Atlanta airport when Person A came in to use the facilities and Person B came in to kill Person A. Through the crack in the stall door, Adam was able to get a very good look at the killer before he put his feet up on the toilet and pretended he was not there. The killer leaves and a couple of minutes late, Anna Martin comes in.
As mentioned, Anna works for the British MI-5 but is stationed in America's southeast while involved with a multi-nation taskforce to stop a very nasty organization called the Radical Liberation Operation (RLO). The murdering Person B was one of the RLO operatives she was tracking but exactly which one she did not know.
Which is why after the murder she needs Adam to identify the man and that is why she has to stick to Adam like glue or, more appropriately, like a very affectionate girlfriend. This explains why Adam is thrown into all sorts of dicey situations and Anna is there to save his backside more than one. To be fair, though, Adam is not a total fish-out-of-water and why he is not a trained operative, he is not stupid and life-and-death situations can bring out hidden qualities.
Adam Levy is described as having dark brown hair, dark brown eyes, trim, "good looking next door neighbor kind of chap". He has a sister named Miriam who is unmarried with a nine-year old daughter. He has a brother Daniel is an assistant Rabbi in the Atlanta area.
Anna Martin is Scottish, one of many children in an Orthodox Jewish family, who grew up in Edinburgh but has worked hard to lose most of her accent. She is a natural red-head but often changes her hair color as a disguise. Described as very lovely and quite athletically built, Anna need to stick close to Adam does not both him in the least.