American Chinese Ding (Cherrie Ying) studies drama in Beijing. One day, she helps her friend chase after her boyfriend, running vigorously on a Beijing street where she bumps into Dong (Louis Koo). The next day, Ding visits Dong, who, strangely enough, denies their acquaintance. Dong's buddy Dr Ching diagnoses his erratic behaviour as the protection mechanism of human brain. The only way to lessen the pain is to erase or repress happy memories.