Execution: Escape from Furnace 5

Alex Sawyer has escaped his underground nightmare to discover the whole world has become a prison, and Alfred Furnace is its master. Monsters rule the streets, leaving nothing but murder in their wake. Those who do not die become slaves to Furnace's reign of cruelty. Alex is a monster too. He is the only one who can stop Furnace but in doing so he could destroy everything. Is he the executed or the executioner? Who will die? All Alex knows is that one way or another, it all ends now.
Execution is an Escape from Furnace book from Alexander Gordon Smith.