We follow the story of the probably adopted Elena – although no one is certain of this, not even Elena – whose parents have moved from Belarus to Romania under Ceaușescu's régime. They are absolutely against their daughter marrying her Jewish friend Jacob because they say they fear he would move with Elena to Israel. However, Elena's wishes triumph and she marries Jacob – she a nuclear scientist and he an engineer – and although they move to Israel for a brief period, their aim is to escape to America, with their son Alex, for better opportunities. They succeed in crossing the Atlantic via Italy.
In the US Elena Anglicises her name to Helen and the couple live a much better life, hoping that Alex will have the 'brilliant future' of the title. When Alex – who has a penchant for foreign women – starts to get serious with the French woman Marie there is a replay of Elena and Jacob's problems in Romania: the parents (particularly Helen) fear that they will lose Alex because Marie will inevitably want to return to France.
Un brillant avenir is a novel not just about national differences and languages and the misunderstandings they cause, but of different age groups misunderstanding each other, of people's behavior being misinterpreted, and how much it can affect people. Helen above all is too sensitive – a neighbor just has to make a joke and she takes it the wrong way, she can be very hurt by something Marie has said without thinking, and she nurses it for years, letting it fester. Sometimes she's right to speak out – as when she strongly objects to an anti-Semitic joke one of her guests cracks – but a lot of the time she simply gets things wrong.
She's usually wrong about Marie, but then of course she's jealous of her – jealous that she might take Alex away, jealous that Marie has a PhD and Alex doesn't, jealous of young women's freedom. She even at one point imagines Marie as a female satan – but through the years she comes to understand her more, sees her even as someone she might have been herself if an earlier age had allowed it. Mother-in-law and daughter-in-law reach a mutual respect that represents a kind of love.
There's some impressive psychology at work here, particularly with Cusset unpacking the minutiae of mistake.