The main conflict in the book Twilight is that seventeen year-old Bella Swan falls in love with her mysterious classmate and vampire Edward Cullen. Edward feels conflicted on the morality of having feelings for and developing a relationship with a human girl. He feels he may put her at risk of injury or death if they are to become emotionally close to one another. Bella is not afraid of Edward and the risks she might face in dating a vampire and befriending his equally undead family. Edward feels a special interest in Bella as he has a mind reading ability but is unable to read her mind. Throughout the book, his special interest in Bella leads him to save her from a number of accidents that might seriously harm her. Edward also admits that the smell of Bella's blood is highly appetizing, so he has a difficult time being around her for fear of biting her.
Throughout the other books in the series, the trouble of Bella's humanity continues to be a driving conflict as she is constantly at risk of harm.