Da Jin and Xiao Jin are sisters. Xiao Jin secretly falls in love with the eldest brother who lives next door, but the eldest brother doesn't know about it. What about the second brother? He likes Xiao Jin. Da Jin tells Xiao Jin: "Girls should be reserved." He studies the eldest brother Lin Quan from a psychological point of view. Da Jin first studies Lin Quan's childhood things, and then interviews his mother. His mother answers his questions in completely different ways, which makes her laugh and cry. Da Jin invites Lin Quan to meet her. Initially, Lin Quan refuses to meet her, but later, when he hears his mother saying that she is investigating him, he agrees to meet Da Jin in a very angry state. The second oldest, Lin Fan, and Xiao Jin are worried that something might happen to them, so they decide to go first. Sure enough, Lin Quan has bad intentions. He forcefully kisses Da Jin, and Xiao Jin, who is peeping, is so shocked that she falls off. The four of them face each other and are very embarrassed. In her passion, Xiao Jin expresses all her love to her. Lin Quan is stunned, and Xiao Jin runs away crying. Lin Fan cannot bear to see Xiao Jin sad, so he fights with his brother. From then on, the four happy young people are trapped in the pain of love together...