Kei (Leo Koo) has just wrapped up a big contract for his company (though it's never clear what kind of work he does). He decides to take a well deserved vacation, to go and visit his girlfriend June (Anita Chan) in Japan. He hasn't seen her in a while.
When he arrives he finds her cold and distant, and soon learns the awful truth: She has hooked up with his good friend Sam (Sam Lee), a fact made all the more sad, because he told Sam to take good care of her while he was away at work. Depressed, but unable to deny that they have grown apart, he wanders the streets.
He runs into Kiki (Shu Qi). She works in a local diner, but dreams of becoming an actress. She's a happy optimistic girl and the customers love her, because she always has some comforting words for them.
Kiki makes af deal with Kei. She'll be his girlfriend for 24 hours, to help him through the rough times. The two spend the day together, and naturally they start to develop feelings for each other...