Emma and Simone are on their own ... and descending into the very depths of Hell.
Eight years on from the end of BLUE DRAGON, Book Three of Dark Heavens, Emma and Simone face a new threat. Simon Wong's demon associates have linked up with Kitty Kwok and the Hong Kong underworld, and have kidnapped Emma's students.
At the same time, the King of the Demons is allowing his children to torture Leo, in hopes of drawing Emma and Simone into Hell too and into his hands. Emma and Simone must defeat the demon-underworld alliance, then enter the gates of Hell to free Leo -- without being captured and defeated themselves.
And Xuan Wu, lord of the Northern Heavens, is unable to help them. He can no longer take physical form ...