The young couple, David Yuen and Wong Wai-ling, have a chance encounter on a bus. When David gives up his seat for Wai-ling, the bus jolts, and Wai-ling accidentally leaves a lipstick mark on David’s face, leaving a lasting impression on both of them. Encouraged by his colleagues, David returns to the bus stop to wait for Wai-ling and eventually meets her again. They begin dating. Wai-ling wants to test David’s feelings for her. After a series of twists and misunderstandings, the two reconcile, and at the same time discover that Wai-ling’s single mother and David’s single father already know each other, and have also fallen in love.