The City of Flame and Shadow (The Horizon Chronicles #3)

The mortal world is at risk. Darkness brews in Horizon. Hades is mustering the full force of his power with the help of the Helm of Darkness, and he releases an apocalyptic nightmare onto the mortal word. Alexa and Milo must travel to another dimension, a world of flames and ash and shadow, in search of a secret weapon that can destroy Hades.
While Alexa realizes exactly how much she’s willing to risk for Milo, can she harness her newfound powers to help save the mortal world?