Freshman Ji Yulmu looks like the ultimate bookworm: thick glasses, baggy clothes, and a quiet, studious vibe. But inside her little green notebook? Nothing but filthy fantasies and kinky stories she’d never dare say out loud. That is, until her campus crush, upperclassman Jeong Wook, finds it. Instead of judging her, he’s thrilled, and he wants to “talk” about her writing. Now Yulmu is getting dragged into Wook’s mysterious X-Games club, where nothing is as innocent as it looks… and everyone, from Cha Ji-un to Seon Inhyeok, wants to play.