Danielle Henderson was Dustin's little sister, not sure if it should be considered little since it's only a 1 year difference, but he prefers it that way. She had to come to stay with his mom and him because their dad died, Dustin never told any of his friends about her, so he was worried about what was gonna happen. Maybe he was exaggerating because the boys did take a good liking to her. Especially Mike. (Following season 1!, chapter 1)
5 parts