Ruby and Arcus face a more dangerous enemy than they could ever have imagined. Once Eurus opens the Gate of Light, darkness will be unleashed upon the world for all eternity. The Frostbloods and Firebloods have formed a tentative alliance, and are now preparing for war - but Ruby is the only one who can prevent the catastrophe which is coming. With the blood of night running in her veins, the line between good and evil becomes blurred. Ruby must be strong enough to face the darkness within - or else everyone she loves will be swallowed up by the night...