This is the second book of The Guardian Of Morning Series. In case you've never read the review of the first book, here it is: http://booksandsweetepiphany.blogspot.com/2013/03/review-of-5-morning-rising-by-samantha.html
Picking up shortly after the events in Morning Rising, Darkness of Morning finds Kara and Dylan drawn back into the world of Inbetween in hopes of stopping Alster and the new King. Though they believe Alster is planning an assault on the Daylands, bringing Dylan over to his side is his true goal. As the girls and their friends plot to bring down Alster, Dylan's moods shift dangerously testing both her relationship with Kara and her commitment to saving the Daylands.