Dead Beat Book by Leigh Bardugo

Following the chaotic events of Hell Bent, Galaxy "Alex" Stern faces her final and most dangerous trial when the cracked-open gates of Hell release demons onto the Yale University campus and the streets of New Haven. To seal the portal permanently, Alex must lead her allies against corrupt occult powers and an ancient vampire while navigating her complex connection with Darlington, who has returned from Purgatory half-demon and cursed with highly unpredictable, dangerous magic. Told through dual perspectives for the first time, this explosive trilogy conclusion forces the team to confront the darkest secrets of the secret societies to save both the living and the dead.