Night Terrors - Hound of Hades, #4

How do you fight a nightmare that's literally going viral? Manhattan is under siege. The invading army is a plague of waking nightmares: the weapon of choice for the new goddess in town, who has just declared an end to Hades's power in New York City. Needless to say, Mal is pissed. With half the mortal population scrambling to flee, and the other half bringing real weapons to the streets to fight the monsters in their heads, the city plunges toward utter chaos.
But Mal's race to save Hades's last scrap of territory will turn her against her oldest friends, unearth a secret the gods themselves have kept buried for thousands of years, and test the limits of an alliance she thought was unshakable.