A Guardian goes missing. A visit to the Island by his fellow Guardians leads to Kemuri, Temperance, and Diamond searching his world for him. They learn that he is protecting something known as a Piece, one of nine, that is now missing, and that the only creature to ever challenge Kemuri may be responsible. 

The boys struggle with their loss and grow apart during the months before Winter begins. As the feelings of guilt and sadness grow, tensions reach a breaking point with a visit from an old friend. Just when they begin to find ways to move forward, they learn that Magnes is no longer the greatest threat to their world. They return to the Island, where they are told previously unknown facts about creation and how the world broke. They learn about the Pieces that, when assembled, create the Key that will unlock the source of evil in the realm of the living. Demons, sorcerers, wraiths, and creatures known as esfetials are unleashed into different worlds to search for the Pieces in hopes of reigniting the War. 

An ambitious werewolf pack feuds with Tremor’s, deciding the best way to establish themselves is to take what they want. 

Colleen Zhang has battled to recover from the vicious attack that nearly took her life. However, the physical pain pales in comparison to the emotional and psychological as she struggles to leave her former life as Christine Lei behind her to keep her family safe.

Unbeknownst the Maven, Mikaela has discovered someone spying on Asylum. She manages to find a way to mask her activities and locates the Horsemen. Shadow prepares his Inmates for an attack, determined to end the struggle permanently. 

Guardians from several worlds work together to prevent the Pieces from being found. Unfortunately, they are bound in ways that may cause them to fail. Knowledge is power. And knowledge hidden for millennia has somehow been discovered. 

The past returns and retributions are declared. The battle between good and evil reaches new heights when more than one world is at risk. Life itself may be compromised. Can evil remain contained?

Or is everyone Hellbound?