Most good stories start with a fundamental list of ingredients: the initial situation, conflict, complication, climax, suspense, denouement, and conclusion. Great writers sometimes shake up the recipe and add some spice.
Exposition (Initial Situation)
The Marquise de Merteuil writes to Valmont to put aside whatever unimportant thing he's doing and to return to her so they can plot a way to humiliate the Comte de Gercourt, who's just jilted the Marquise, by seducing Gercourt's young fiancée, Cécile de Volanges. Valmont has his own plan, however: the seduction of Madame de Tourvel, a faithful and religious married woman. Meanwhile, Cécile has returned home from the convent in preparation for her marriage to the Comte de Gercourt.
Nothing especially dramatic is happening yet. This is just the setup for rivalries, bitterness, and double-crosses later. We now know what the principal characters want and the general direction they'll be headed.
Rising Action (Conflict, Complication)
Valmont puts the subtle moves on Madame de Tourvel. He's playing the reformed-libertine-who's-found-God angle. He doesn't win the married woman's heart, but he convinces her that he's not such a naughty fellow as the rumors say. He certainly doesn't deflate footballs before playoff games.
Cécile's thoughts of marriage become complicated when she falls in love with her music instructor, the Chevalier Danceny. He likes her too. Valmont offers to help them correspond in secret. This allows him to put the Marquise's plans into action.
Valmont is super smooth, even if to us he's also super creepy. He's slow and calculating in his plans, but he makes progress. The main obstacles he faces are Madame de Tourvel's virtuousness and Cécile's innocence.
Climax (Crisis, Turning Point)
Valmont Victorious
Madame de Tourvel begins to fall for Valmont, who's turned on the charm and promised his pure love. She flees from him to avoid temptation. He follows, threatens suicide if she won't have him, and she gives in.
During this time, Valmont also has used his proximity to Cécile and her trust to enter her room at night. He rapes her. The Marquise de Merteuil tells Cécile not to fret and that Valmont could be a good friend to her if she tries to please him. She agrees.
At this stage, two relationships can never be the as they were. Madame de Tourvel has cheated on her husband and Cécile cheated on Danceny. Valmont's completed his two projects. At the Marquise's request, he abruptly dumps Madame de Tourvel. Where do we go from here?
Falling Action
The Marquise reneges on her promise to sleep with Valmont and they viciously turn against each another. The Marquise tells Danceny that Valmont has had sex with his girlfriend. He challenges Valmont to a good old-fashioned duel and mortally wounds him. Before Valmont dies, he gives Danceny all the letters he has, exposing the Marquise's evil plans to corrupt Cécile and humiliate her ex-suitors, as well as frame a man for raping her.
Madame de Tourvel, destroyed by guilt and by Valmont's betrayal and death, dies Senator Amidala style—from a broken heart.
The falling action is quite literally the falling into death of two major characters. The remaining will meet their fates in the resolution.
Resolution (Denouement)
No happy endings here. Cécile returns to the convent, but won't tell her mother the reason. The Marquise, her sins now known to the public, flees Paris and contracts a disfiguring case of smallpox. Madame de Volanges writes to her friend (and Valmont's aunt), Madame de Rosemonde, seeking answers for her daughter's despair and decision to become a nun. Danceny travels to Malta to take vows of celibacy.