Neon Gods (Dark Olympus, 1) by Katee Robert

He was supposed to be a myth.
But from the moment I crossed the River Styx and fell under his dark spell... he was, quite simply, mine.

Society darling Persephone Dimitriou plans to flee the ultra-modern city of Olympus and start over far from the backstabbing politics of the Thirteen Houses. But all that’s ripped away when her mother ambushes her with an engagement to Zeus, the dangerous power behind their glittering city’s dark facade.

With no options left, Persephone flees to the forbidden undercity and makes a devil’s bargain with a man she once believed a myth... a man who awakens her to a world she never knew existed.