"crossing" Is the second book in a series of three (the first one titled "undying" and the forthcoming last one titled "fading"). The three novels are a representation of the three parts of life: birth, life and death. While not required, "crossing" will be easier to understand if you have read "undying", which introduces the characters.
In "crossing", Matt struggles with depression. Even though he has everything he could possibly want: a great job, a beautiful partner and good health, he is unable to shake a cloud that follows him wherever he goes. As the cloud gets darker and his emotion more negative, Sandy does everything she can to help him, even though she herself is struggling with her own emotional plight: how to prove that she is alive.