Rebecca 'Bex' Wilson is a freelance agent for MI6.
Kieron Mellor is a teenager who works with Bex Wilson.
While Mellor is the star of the series as most activity revolves around him, Wilson is the actual, official agent and Mellow would not be doing what he does without her; therefore, he gets named first in the fact sheet at the top and she gets first billing with Mellor right after in this writeup.
I want to mention here, now that I've got the introductions out of the way, that the name given this set of adventures, A.W.O.L., does not mean anything like the traditional absent-without-leave; it instead stands for Agent Without License. Now, since Wilson is working on behalf of and with the approval of MI6, the AWOL here definitely indicates Mellor. He is not licensed, or approved, or even known about by that British spy organization.
A tad more information then about the pair, starting with Wilson. She and a fellow, likely ten years older than her approximate 25 years of age, are a team of contract operatives who bid on and are given one-shot missions. The pair actually contract with a sub-group in MI6 known as SIS-TERR - the Secret Intelligence Service's Terrorist Technology-Enhanced Remote Reinforcement. If they pull a job off successfully without blowback, they are more likely to get another and the more they do, the higher up the food chain they would progress. As we meet them they have had several successes so they are in good standing but not so good that they do not worry about making sure more work comes in.
Mellor is, as mentioned, a teenager, self-described as "nearly six feet tall [with] black hair and my skinn looks like I've for a tan. I haven't - my dad's from Mauritius - but that's the only thing about me that looks Mauritian. Everything else I get from my mum. I identify as a greeb but looking at me you'd say I'm an emo or a goth." [Note those last two I sort of knew about but the first, not so much.]
So now a brief explanation of why Wilson and Mellor are working together.
Wilson is out in the field in Mumbai, India. Bradley is back in England, Newcastle specifically, monitoring things via the Internet with the use of a really cool pair of high-tech glasses and an earpiece, talking with Wilson and seeing much of what she sees and passing vital intel as needed. When we meet them, Bradley is in a food court in a mall getting something to eat. Mellor and his best bud, Sam (also a greeb and proud of it) are in the same food court trying to figure out how to get into a concert they cannot afford.
Miller does not set out to get involved in the spy game, although he definitely chose to do something a tad foolhardy that would lead him to become immersed in it so he has to shoulder some of the blame. Mellor notices a man sitting near them stand up from his table and almost instantly get silently abducted by two strong, scary-looking dudes. As they whisked him away, Miller got the crazy idea of following, telling Sam, "I want to see what they do when they get to the car park. If they throw the man into a police car or an ambulance then we'll ignore it; if they put him in the back of some anonymous black executive car then we'll tell someone".
Along the way, he notices the subdued man had dropped a Bluetooth earpiece and dark glasses. Miller scooped them up on his way out thinking - and this is rather telling about Miller - "If the man was OK then he might want them back. If he had vanished, well, the stuff might fetch a few pounds at one of the shops Kieron knew in the old High Street, no questions asked". A tad mercenary mixed with charity. But then the two kidnappers toss the fellow into a van and drive off and Miller heads back to meet up with Sam and ponder what next.
That what next will involve putting the earpiece in his ear and putting the glasses on and after a moment he can see in a kind of a projection a scene from somewhere else (turns out it was Mumbai) and hears over the earpiece the voice of a woman chiding someone named Bradley to "stop feeding your face. I need your help". That is how Miller would be introduced, sort of, to Bex Wilson and vice versa.
After that, things get a lot of fun.