A fortress besieged is a metaphor for marriage: everybody out wants in, and everybody in wants out. Considered one of the masterpieces of twentieth century literature, it is littered with memorable quotes and witty observations.
It follows the feckless Fang Hongjian, who is returning home to China after running out of money while studying abroad. Despite enjoying financial support from his family, Fang has neglected his studies and bought a fake degree.
On board the Vicomte de Bragelonne, he meets the pretty and unmarried Su Wenwan. He also meets the tanned and voluptuous Miss Pao, whom Fang pursues with some success during the voyage. When the boat reaches Hong Kong, Miss Pao disembarks into the embrace of her fiancé, and Fang realizes he has been used. This is just the beginning.
It has been argued in the LA Review of Books that Qian Zhongshu was Nobel Prize material for this novel alone. https://lareviewofbooks.org/article/a-monument-to-what-might-have-been-qian-zhongshus-fortress-besieged/