Chimera by Rob Thurman
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Ten years ago, Stefan Korsak’s younger brother was kidnapped. No one knew who took Lukas, or why. He was simply gone. But not a day has passed that Stefan hasn’t thought about him. As a rising figure in the Russian Mafia, Stefan has finally found him.
But when he rescues Lukas, Stefan must confront a terrible truth – his brother is no longer his brother. He is a killer. Trained, brainwashed, and genetically transformed into a flesh-and-blood machine with only one purpose: assassination. Now those who created him will do anything to reclaim him.
As Stefan grows closer to his brother, he realizes that saving Lukas may be easier than surviving him...