Chris Ryan 
Endgame 

»Don’t come after us … remember the first thing I ever taught you — that your first duty is to stay alive»
For some time now, Zack Darke has been operating solo, in total secrecy, for a shadowy government organisation.
When his handlers are abducted by somebody with a serious personal vendetta against him, Zak has no choice but to go after them. And heading across the world to find them — into danger like he»s never known — is something that, this time, he cannot do alone . . .