Zak Darke is an agent with British Intelligence.
Exactly which agency he works for is not known and his boss seems as mysterious as his shadowy bureau. Zak was warned, friendly enough but sincerely, that if he tried to find out, no one would help and no one would believe him. This last part was mostly likely because being a teenager, his questions would be chalked up to a vivid imagination at best and delusion at worst. The man did tell him that Darke could call him Michael if he wished - not that it was really his nice, just that Darke could use it for him. And the department this Michael worked for was so secret few would recognize its name, even the Prime Minister.
There would be few taking his side, either. When his parents died of food poisoning while attending a conference in Nigeria, Darke was left to live with his aunt and uncle, good people but strict and not really prepared to have another mouth to feed and body to clothe. Except for his cousin, Ellie, Zak was largely alone. He did not have any close friends due to being new to the area and being smart than most his age.
When he was approached to join the organization, he demurred. Life would soon bring him around, not the least reason being a chance to learn how his parents' deaths were no accidents. Joining meant leaving behind everything he knew which, except for his cousin, was not much of a loss but totally abandoning everything was a huge step.
His training was conducted by two people assigned him by Michael, both in their mid 20's. One was a female named Gabriella and the other a male called Raf. It did not take Darke very long to realize the names, like much of his new life was going to be, were not real but were versions of Gabriel and Rafael, letting him know that in addition to training they were his guardian angels.
Darke is codenamed Agent 21. Raf was Agent 16 and Gabs was Agent 17. These facts lead Darke to believe that the group to which he belonged was not that large but it also made him wonder how many of those numbered higher were still around to use the designations.
Becoming an agent at such a young age will totally change his life forever but no matter what training he might get or how much experience he might acquire, he is still a teenager with a teenager's look at everything.