Dehali (The Tartarus Chronicles)

Tartarus has become unstable. Having been pulled through a mysterious portal into the underground world of Tartarus two hundred years in the future, Gunther Leuschen is on the verge of discovering how to reverse the portals and return to Earth. Forced to team up with a group of con artists and criminals, Gunther and his friends are being hunted by the technologically and genetically enhanced Guardians from the city of Elysium, as well as the military of the city of Dehali and their robotic soldiers. But his greatest challenge may come from the forces that strive for his beliefs, and his soul.