Edward and Bella are highschool sweethearts in their junior year. Bella has a big brother called Emmett that is going out with Rosalie, the queen bee of the school. Who is surprisingly not bitchy. Rosalie has a twin brother called Jasper and he is dating Alice, Edward's sister. After a date one night Edward goes missing. His car is found at the bottom of a small cliff. He's not in it. It's said that he lost control of the car at a bend and he probaly jumped out and was so seriously injured and not thinking straight that he just crawled away from the wreakage and died.
At the same time the best doctor in Forks takes a temporary leave. The Cullens don't leave and after a couple of months Carlisle comes back to work. On her birthday Edward was going to take her to see her mother in Pheonix as a surprise. The tickets appear on her desk a week before her birthday. With a note in Edward's handwriting. At school she tells Alice about it but she tells her that Edward bought those tickets before he died and Charlie probably forged Edward's handwriting to stop her from moping over him and gave her the tickets. Bella knows that Charlie wouldn't have been able to forge Edward's neat handwriting.
So when she gets back from Pheonix she starts investigating her sweetheart's supposed death. When her brother finds out he begs her to leave it alone but when she doesn't he gives up. She eventual finds that his body had never actually been found and she drops school. She gets a job as a journalist in the Port Angeles newspaper and gets her own apartment. She searches the area for clues and finds a wedding ring under a stone near the crash site. She recognises it as Carlisle Cullen's. So she starts snooping around the Cullen's place.
Not telling the ending, sorry.
(Note: This is only a rough outline, it may change slightly or drastically depending on how I feel … or you feel.)