In order to review for the exam, Ali (played by Alex Fong) and his friends moved into the remote unit 999. However, not long after moving in, Ali discovered that all the supernatural events that science could not explain seemed to be happening around him. The playful sounds in the empty corridor, the bloody man, the looming footsteps, these strange things that only Ali noticed, are they reality or fantasy? By chance, Ali met a strange girl named Xiaoyu in the corridor. Xiaoyu told Ali that she and her elder sister Lucy and second sister Mary lived in unit 666. As time went by, Ali gradually fell in love with the gentle and lovely Xiaoyu. However, what he didn't know was that Xiaoyu and her two sisters were all dead ghosts for a long time, and Lucy and Mary, who survived by sucking blood, regarded the good man Ali as their next target.