What is the book 'kissed by an angel' about?

its about a girl, Ivy, whos boyfriend, Tristan, gets killed in a car crash and someone is also trying to kill her and she starts to see a "sparkle" and it turns out to be her boyfriend because he is still on earth as an angel. he has to help her find out who is trying to kill her and also if his death was really just an accident!!!

He helps Ivy find who the murderer is but once he finished his mission, He will have to leave his true love.