Love. Betrayal. Revenge. Lucifer has escaped from purgatory. Darkness descends on both Horizon and the mortal world. The Order of the First is the on move, systematically turning angels against angels. Their numbers continue to grow as chaos and destruction overwhelm the Legion.Meanwhile, Alexa is trapped in Tartarus, the impenetrable and inescapable angel prison, knowing all too well that she's responsible for Lucifer's breakout. But can she find a way to escape her prison to fight the greatest evil she has ever faced? Worse, Milo has sacrificed himself to save the angels from his father's deadly wrath. Will Alexa ever see him again? If so, is he allied with his father? Can she still trust him? Or is he truly lost?The stakes are higher than ever in the last installment of The Horizon Chronicles series.