Towards the end of their summer holiday, a group of high school students’ peaceful lives are disrupted. Someone named “Admin” adds them to a chat group and forces them to play a killing game. Before they find and remove “the target”, whose identity is unknown, anyone in the chat group who does not reply to other members’ messages will die instantly. Panic strikes as students in the class suddenly die one by one. Ho Hei Yin, a gentle and simple student, fights with “Admin” to protect his precious friends. In order for the class to survive, Yeung Yuet Ying vows to uncover the identity of “Admin”, even if it means putting herself in danger. A cynical Shek Hiu Yeung aims to save as many classmates as possible by locating and removing "the target” quickly. While the trio try to save others, some people show their true colours under pressure. One of them uses the game to kill others in order to win. Another one kills his friends brutally for revenge. One uses his friends as pawns in order to survive…The place where they should enjoy their youth is turned to a scene of carnage.