Oblivion — Karolyn Cairns

Lindsay Morgan and Jace Turner had their whole lives ahead of them until one horrific act changed everything. Lindsay has to learn to live without Jace and come to terms with his murder. Jace finds himself in another place, off the beaten track from Heaven. A place called Oblivion. Determined to get back to his girl and make his murderer pay, Jace realizes the meaning of life and love.
With help from his mentor named Merrick he learns the secrets of Oblivion. Between dodging demons and creatures called deadheads, he learns the ropes to get back to his girlfriend in time to save her from the one who killed him.
Lindsay agrees to go after Jace's murderer, determined to get justice, never realizing every step brings her closer to death's door. She soon finds out the painful truth that you can't know everything about someone in a shocking twist after his death. Jace has come back to make things right, for his girl, his family, and the one thing he can't take back. With the help of the town's other ghosts he sets out to avenge his murder. Reaching out to Lindsay for one last goodbye, he shows her love really does last forever.