This is the second novella in the Group Fifteen Files written by Mark Dawson with the help of some of his peers. This book was better than the 1st, which wasn't bad and now I'll go the last as of this date, Little Sister. All of these can be read for free on Kindle Unlimited at this time.
Witness X starts out with an attack on a woman for no apparent reason but when MI5 starts digging into everything they bring in the people that pulls the trigger, Group Fifteen. Control, the man that oversees Group Fifteen calls for the one man that can get to the bottom of everything, Twelve, or the under suspension Bryan Duffy. The reason Duffy is brought in is because of this attack was personal. The attack was carried out by a North Korean agency equivalent to Group Fifteen and espionage was a reason for them to kill anybody that would get in their way.
Dawson and Mariani pack 104 pages full of action and very little wasted space. So far if this is a genre you like then I suggest this little novella series as "Group Fifteen Files, Volume 1" be added to your reading list if you want something quick to read.
Witness X by Mark Dawson and Scott Mariani
A Group Fifteen Novella (Group Fifteen Files Book 2)