A girl that the three shadowhunters grew up with suddenly returns to the institute. She has no explanation. Arco disappeared overnight, the night before Alec turned 15. She's been missing for over 5 years and refuses to tell anyone of what had happened to her. Disclaimer: I do not own The Shadowhunters (very unfortunate, I know) or anything apart from Arco and her story line. This is an original story by CliffordOnFire {Season 1 from Episode 4}