The Death of My First Assignment (Death Series)

Life after death has way too many disadvantages.  Katie's recent trip to the beyond and back again has left holes in her memory. Sent back to help high school student Serena complete an unfinished task on Earth so she can pass on when she dies, Katie must first figure out exactly what that task is. Someone conveniently forgot to tell her. And those holes in her memory suddenly become a real liability when the soul-stealing wraiths show up along with blond, tall, and mysterious Martin, who seems to know a lot about Katie's missing past.  Somehow Katie has to help Serena, keep them both safe from the wraiths and figure our what the heck is going on...in time.