They start a clandestine romance. He is the 27 year old son of a Chinese business magnate, a young man of wealth. He is quite in love with this girl, but she is still so young that the whole affair seems more a general discovery of the world, and above all, an escape from her family, from her manic-depressive mother.
Surprisingly, this slight story sold a million copies in forty-three languages. The novel has been called "autobiographical," which may have helped sales, but of course it is not an autobiography, but a fictional novel (that perhaps contains fragments of Duras' life, but set in a new context and seen from new perspectives). It is told in a fragmentary way, jumping from memory to memory, digressing, and then returning to the story by repeating certain parts. It is as if we are listening to an elderly person lost in memories of the past - but that probably is all part of the clever style.
I have read The Lover in the English translation by Barbara Bray (Pantheon Books). The novel was made into a film in 1992, also under the title The Lover, with Tony Leung and Jane March.