Those Classmates who Suddenly Disappeared

An unexpected journey took a group of university students into a secret room from which, upon returning, they began to disappear one by one. In order to unravel the mystery, they joined forces, traversing heaven and earth, diving deep into seas, crossing the farthest corners of the world, and even daring to time travel, only to find that behind each puzzle lay yet another. — Description from novelcodex.org