Bella Swan is the Fork High bad girl. She goes to parties, plays round with boys, and rules the school. She's dating the guy that rides a motorbike. When Edward Cullen, the new guy, turns up, she hates the way she's so affected by his presence alone, and does everything in her power to fight whatever is going on. But it's impossible to fight love, and Bella finds herself being turned back into the girl she once was.
Whether she ends up good or bad is another question entirely.