This I guess is a three book in one. I was wondering why it was taking me forever to get through it. Duh on me until I realized. Anywho, here's an outline of the books.
Kissed by an Angel is the story of Ivy and Tristan. Tristan is a swimmer on his school's team and extremely popular. Ivy is new to the school. This book follows their story of how their relationship evolved, ending with Tristan's tragic (and somewhat mysterious) death.
In The Power of Love, Tristan, now an angel, is dealing with the fact that he's dead and an angel. He is helped by Lacey, another angel, who urges him to figure out what his mission is. He's overcome with the loss of Ivy, knowing he'll never be with her again. Ivy, meanwhile, is mourning Tristan while everyone around her is telling her to move on. Throughout this story, Tristan comes to the conclusion that someone is out to get Ivy for something she saw but shouldn't have.
In Soulmates, Tristan continue's on his mission of saving Ivy's life. She regains her belief in angels, which she lost after Tristan's death. In regaining her belief, she is able to communicate with Tristan to help figure out the details as to who is after Ivy.