男主季白（王凯饰）和女主许诩（王子文饰）是看似关系冷淡的师徒，却是生死相依的战友，更是相互钦慕的爱人。季白是深沉冷酷的资深神探，许诩是一位犯罪心理研究的天才新人。两人在联手破获一桩大案之后，季白对这个单纯睿智的爱徒心生爱慕，奈何无论他如何明追暗夺，这个如“蜗牛”般迟钝的女孩，就是收不到爱的信号。在二人“谈情说案”之际，也是一段极致甜蜜、却也极致艰险的追凶之旅。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.