Adam Crest is an agent of MI6.
He will be, at any rate.
Our introduction to him comes on a very rainy day in 2019 when he stops at a garage which doubles as a small convenience shop. He is looking for a sandwich to take with him as he headed home. He would never eat that ham and mustard. He would find a dead body that apparently some powerful people did not want discovered yet - or ever - and that would be how Crest gets jabbed in the neck with a hypodermic and wakes up at home two days later as if nothing had happened. Adding to the mystery is a "tall slim woman with long black hair down to her waist" who was disappearing through his bedroom door with a cheery "Ciao darling, see you again soon" which might have sounded inviting and intriguing except Crest has no idea who she is or why she was with him.
Crest at the time was a "field-based middle manager" for Comm-Sec UK, selling security equipment and services to company all over the country. He has been with that company for a couple of years and had recently found it a bit boring and very mundane, which is on the negative side, and very safe and free from Taliban trying to kill him, which is plus.
The Taliban part had been for some time a factor in his life in the SAS working closely with the Intelligence community, up until a particularly unusual mission to take out some arms dealers had resulted in several of his men getting killed, Crest getting stabbed in the leg severing the femoral artery and nearly dying, and then finding the whole shebang being majorly hushed-up.
That was when he decided boring was not so bad and he got out of the military and found a simple job and a single but still very contented life. Until he found the owner of the garage dead and someone wanting to keep it on the down-low and willing to go to some trouble to keep it that way.
Unfortunately for 'them', Crest is no little miffed and curious and perhaps a bit too bored with his life so instead of taking the unspoken hint and letting it go, he decides to find out the truth. Along the way, those he was seeking will find out that not only is Crest a determined man, he is a clever and intelligent man. More importantly, when they take off the gloves to stop him, they will learn that Crest has been trained by the very best that the SAS had to remove those who got in his way - permanently, if necessary.