楊怡
During his police work, Kingsley meets policewoman Tsui Siu-Lai (Tavia Yeung) who acts as a liaison with the Regional Crime Unit and Kingsley. The rational Kingsley evaluates that he has fallen in love with Lai because of a neurotransmitter called phenethylamine. However, owing to the huge difference in their family backgrounds and life values, Kingsley fails to tackle their ever-changing relationship problems with formulas. In the end, due to various life changing experiences, Kingsley realizes that love cannot be rationalized and finally admits that his feelings to Siu-Lai are true.