[1] Freelance mercenary Court Gentry is tasked with assassinating former Serbian general Ratko Babic at his compound in Bosnia and Herzegovina.

While infiltrating his house, Gentry discovers that it is also a way station for young girls waiting to be transported east and sold into sex slavery.

Liliana informs Gentry about Captain Niko Vukovic, a police chief stationed in the nearby city of Mostar who is Babic's associate.

After sending the girl home safely, Gentry goes to Mostar and surveils the police officer, later apprehending Hungarian mobsters sent to kill him.

She had embarked on a personal mission to find her sister Roxana, who is missing and presumed dead or sold into sex slavery.

The Director of the Consortium, Hollywood-based businessman Kenneth Cage, sends security contractor Jaco Verdoorn and his men to Croatia in an effort to dispatch Gentry and Corbu.

The former South African special forces member is also tasked with shepherding the yacht full of trafficked young girls to an auction in Venice, Italy.

Gentry then asks for help from an Italian crime family he had previously worked with in infiltrating the Venice auction, while he instructs Corbu to travel to the Netherlands and coerce a blackhat hacker into accessing the Consortium's financial records.

His boss replies that Cage is an important Agency asset and must not be harmed, but reluctantly allows Court to rescue Roxana and the girls as long as he does not kill the Consortium head.

At Hightower's recommendation, Gentry enlists the services of a group of veterans led by former Delta Force officer Shep Duvall, who used to raid brothels and rescue trafficked girls in the Philippines until they got caught, imprisoned, and later extradited to the United States.

On how he came up with the plot, the author said: "The initial idea for this one began with me picturing the Gray Man on a vengeance mission for something far in the past, but in the process of discovering something unrelated, that’s bigger and more deadly.