Book #13 in the Gray Man series.

Someone is killing the world's leading experts on robotics and computers. A desperate Russian scientist approaches Court Gentry and Zoya Zakharova to ask for their protection, but before they can help, they are attacked by a team of professional assassins.

They escape, but wherever they turn, it's clear that whoever's tracking them is always going to be one step ahead. With a danger of this level, there's no choice but to attack into the threat.

There is one man who may hold the answers to all their questions. But he's gone to ground in a fortress surrounded by a veritable army. If that's not bad enough, he has a new chief of security - Court's old comrade, Zack Hightower.