Lynx

If you stab him in the back, make sure you don't miss. Will Slater is out for revenge in the fourth book in a pulse-pounding series from Matt Rogers, a million-copy bestseller and 'a bright new talent shaking up the genre' (Candice Fox).

Half a year ago in Macau, Will Slater waged war to rescue nine-year-old Shien from the clutches of a hellish industry. He left her with an old government colleague, who promised to find her a foster home and give her some semblance of a normal upbringing. Slater moved on...
 
Now, deep in cartel-infested Colombia, he hears dark whispers of something called the Lynx program – a clandestine division that raises young girls and forges them into sociopathic killers. A division founded by the very same man Slater left Shien with.
 
He drops everything and barrels toward answers. Because if you make Slater a promise, you’d better not break it. The kid was a shining ray of light in his otherwise barbaric reality, and he’ll sacrifice everything to make sure she’s safe.