In bustling 1962 Hong Kong, Chow Mo-Wan (Tony Leung) moves into a new apartment with his wife. The same day Su Li-Zhen (Maggie Cheung) moves in next door with her husband. The two have no real relationship – they pass each other on the stairway going out to get food – until both suddenly grasp that their spouses are having an affair together. As they begin meeting to ponder this shared infidelity, Li-Zhen and Mo-Wan start to feel emotions they are not sure they can, or should, express.