从高中开始就被称为"小柯南"的欧若紫，进入云上学院的第一天，就和最大校董的儿子段琉川结下了梁子。学校突然发生偷窃事件，段琉川自告奋勇调查真相，并请欧若紫协助调查。在段琉川许诺了她三个条件后，欧若紫答应帮忙。有了欧若紫的协助，偷窃事件圆满解决，然而事情并没有想象的这么简单，偷窃事件结束之后又发生了一连串的事件，并且都与一个署名为"Z"的人有关。欧若紫与段琉川欲找出这个人，但每当有一点点线索的时候就断了......欧若紫能否找出真正操纵事件的人？她与段琉川之间的感情，又会发生一些怎样的变化呢？（Ou Ruozi, who has been called as "Little Conan" since high school, develops animosity with Duan Liuchuan, the son of the great director of the school. The theft suddenly occurs at the school and Duan Liufeng volunteers to look for the fact. He asks for assistance from Ou Ruozi. After Duan promises to accept three conditions of Ou Ruozi, Ou promises to help him. With Ou's help, the theft is solved successfully. However, the issue is not as simple as you think, after the theft, the sequence of events happen again and all events are related to a person whose signature is "Z". Ou and Duan try to find this person, but whenever a clue appears, it goes cold...Shall Ou Ruozi find the real operator behind the events? Also, how will the affection between her and Duan Liuchuan change?）