Defiance of the Fall 4

Just as a threat is dealt with, an opportunity presents itself. After searching for months, Zac's forces have finally discovered the elusive Underworld that's both teeming with riches and dangers.

Meanwhile, the armies of the Undead Empire advance on all fronts while the Dominators scheme in the dark. Having endured the Integration in the punishing environment of the subterranean cave system, the trapped warriors of the Underworld could become the key in surviving the incursions aboveground. But first, Zac has to deal with the golems intent on digging to the center of the planet.