What happened to Cassie in April of their Freshman year of high school?

Cassie went missing in the middle of April. When she returned she told Peter, who told Julia, that her home life had been getting worse. Cassie had been searching for her father online, and had found a man she thought could be him in Bangor, Maine. She researched him and his family, and then ran away to Bangor to meet him. When she finally went to his house he said that he did not know her, although Cassie believed that he was lying. She went back to Royston, and to Peter's house. The next day Cassie went back to her own house and confronted her mother. She accused her of lying about her father's death, and of never loving her enough. Cassie then ran off again.