Sai Ming Jun (Anita Yuen) is a single mother who works as an office administrator. But when the company gets taken over, her road suddenly becomes an uphill one. The controlling family's son (Sean Lau Ching Wan) takes an immediate shine to her, and begins to woo her, but she resists. Things get worse when his half-brother (Frankie Lam) shows up. He happens to have a controlling interest in the company - and is the father of Ming Jun's child! Will Ming Jun be able to make it through this twisted maze of family politics and hidden agendas? And will she be able to find a true, honorable love?

Taking place in 1941, Love in a Fallen City centers on Pai, a young woman who has been ostracized by her family for divorcing her rich husband. A local match-maker, Mrs. Hsu, takes pity on Pai and decides to bring her to Hong Kong, under the guise of employing her as the Hsu's nanny, but in reality to introduce her to Fan. Pai and Fan seem to hit it off, but Fan's refusal to marry Pai soon sours things. However, as the Japanese begin to invade Hong Kong, the two begin to realize their true feelings for each other.