Detective Ji Bai and new criminal profiler Xu Xu may seem like an awkward teacher-student pair at first glance, yet they are actually the best partners in the police force, solving one crime after another. Ji Bai slowly falls in love with Xu Xu, yet she is a girl who is as slow as a snail when it comes to love. Just as Xu Xu starts to reciprocate Ji Bai's feelings, the dormant "Angel's Killer" reappears.