The back cover of the book asks: Peut-on passer en une seconde de l'amour à la haine ('Can we go from love to hate from one moment to the next?'), and the answer to that can more or less be found in the title: Schmitt isn't interested in the gentle, idyllic shifts in love's nature as seen in Madame de Scudéry's Carte du Tendre, but in the violent seismic shifts of love's construction and destruction.
Richard is a rich businessman who is in love with the MP Diane, who is also in love with him. They see each other very regularly but don't live together, and although Richard has proposed to her several times, he hasn't done so recently and she feels that he must be tiring of her. When she confronts him with this he agrees with her and proposes that they stop being lovers but remain friends. What the audience doesn't know until near the end is that his pride won't allow him to say he feels just the same and really loves her, so the misunderstanding continues: Diane conceals her emotional pain and her wounded pride and turns it into desire for vengeance.
Diane is an MP with a specific interest in the position of women in society. She talks to two Romanian prostitutes: the first (Rodica) is getting past her prime; the other (Elina) is young and beautiful and has been lured to France with the promise of a university education, although she has no legal papers and has been tricked into prostitution. Within no time, Diane sorts things out legally, gets them off the game and provides them with an attic flat, although of course that comes at a price: that they have to befriend Richard, who needs someone to care for him as he only has months to live because he has cancer. He'll obviously be attracted to Elina, but Rodica (acting as Elina's mother) must fend off his sexual advances.
Richard falls hopelessly in love with Elina (who is also in love with him), but Rodica prevents him from seeing her and tries to give back his increasingly expensive presents to her. Nevertheless, the lovers occasionally clandestinely meet in a public park, although the relationship remains chaste. Even when Richard asks Elina to come and live with him Diane refuses to allow Rodica to let her guard down: Richard will die soon, has no one to leave all his money to, and Elina will be out on the street again when he dies.
And so Richard asks for the hand of the 'virgin' Elina, and it seems fitting that on their wedding day Diane (who doesn't attend) can hear a wedding song, whereas her mother thinks that on the contrary it's a war march.
On the morning after, while Elina is in bed, Diane visits Richard and asks him how the night was, and even if the sheets were bloodstained. Although affronted by the untimely intrusion and highly personal questions from his ex-lover, the new husband is more or less forced to agree that there was indeed blood. Diane tells him Elina has acted her part perfectly without a cue, whereupon she brandishes a dossier with the record of her soliciting, proof positive that she was a practising prostitute, and again we see a tectonic shift of feelings, and the marriage is over.
As the play states, in the emotional world you can't just press a 'Replay' button, at least not as far as Diane is concerned: she's the victim of her own machinations, and pride plays just as big a part in this. When Richard (who is of course in perfect health) finds out about the cancer scam from Rodica and on top of that learns that Elina really does love him, there's a tectonic shift back, although Richard won't unleash the full extent of his hatred for Diane by publicly revealing her treachery out of consideration for her mother, who (unlike Diane) is a good person. The only thing left for Diane is death, she feels.
The final scene is in a mortuary chapel, although it's not Diane's death but her mother's. Here, just before Richard leaves with Elina to begin a new life in another country, Diane accepts the situation and says she wishes Richard happiness. And as he leaves with his wife, he turns his head to Diane to say, his voice trembling with emotion, that he loves her, to which she replies that she loves him. He asks: 'Enfin?' 'Enfin...' 'At last?' 'At last...' (And those are the final words.)
Alfred de Musset is mentioned (by Elina) in this book, and the title of Musset's 1834 play On ne badine pas avec l'amour (a loose modern translation of which I would render as 'You Don't Mess Around with Love') would serve as a very good (but far too late) warning to Diane.
My other Eric-Emmanuel Schmitt blog post:
Eric-Emmanuel Schmitt: Milarepa