Luminosity (Gravity Series #3) (The Gravity Series)

Just when she thought the dreams couldn't get any stranger, Ariel Donovan is transported in her sleep to Dark, a parallel world full of horror and secrets. A dog barks and she knows she must heed his call. During the journey, she finds what she lost long ago, and discovers how important it is in her quest to outsmart the Thornhill Society...before it's too late.