Becoming immortal wasn't supposed to be the easy part. Though Kate is about to be crowned Queen of the Underworld, she's as isolated as ever. Despite her growing love for Henry, Ruler of the Underworld, he's becoming ever more distant and secretive. Then, in the midst of Kate's coronation, Henry is abducted by the only being powerful enough to kill him: the King of the Titans.

As the other gods prepare for a war that could end them all, it is up to Kate to save Henry from the depths of Tartarus. But in order to navigate the endless caverns of the Underworld, Kate must enlist the help of the one person who is the greatest threat to her future...Henry's first wife, Persephone.