The setting is Sweden, around the year 1900. One by one, the Quintet – five singers who comment like a Greek chorus throughout the show – enter, tuning up. Gradually, their vocalizing becomes an overture blending fragments of “Remember”, “Soon” and “The Glamorous Life”, leading into the first “Night Waltz”. The other characters enter waltzing, each uncomfortable with her partner. After they drift back off, the aging and sardonic Madame Armfeldt and her solemn granddaughter, Fredrika, enter. Madame Armfeldt tells the child that the summer night “smiles” three times: first on the young, second on fools, and third on the old. Fredrika vows to watch the smiles occur. Middle-aged successful lawyer Fredrik Egerman has recently married an 18-year-old trophy wife, Anne, a naive girl who loves Fredrik, but isn’t attracted to him. The two have been married for eleven months, and Anne still protects her virginity. Fredrik plots how he might seduce his wife (“Now”). Meanwhile, his son Henrik, a seminary student a year older than his stepmother, is frustrated and ignored (“Later”). Anne promises her husband that shortly she will consent to have sex even though she can’t help recoiling at his touch (“Soon”), which leads into all three of them lamenting at once. Anne’s maidservant Petra, an experienced and forthright girl, slightly older than the teen herself, offers her worldly but crass advice.
Desiree Armfeldt is a prominent and glamorous actress who is now reduced to touring in small towns. Madam Armfeldt, Desiree’s mother, has taken over the care of Desiree’s daughter Fredrika. Fredrika misses her mother, but Desiree continually delays going to see her, preferring, somewhat ironically, “The Glamorous Life”. She is performing near Fredrik’s home, and Fredrik brings Anne to see the play. While there, Desiree notices Fredrik in the audience; the two had been lovers years earlier. Anne, suspicious and annoyed at Desiree’s amorous glances, demands that Fredrik take her home immediately. Meanwhile, Petra tries to seduce a nervous and petulant Henrik.
That night, as Fredrik remembers his past with Desiree, he sneaks out to see her; the two have a happy but strained reunion as they “Remember”. They reflect on their new lives, and Fredrik tries to explain how much he loves Anne (“You Must Meet My Wife”). Desiree sarcastically boasts of her own adultery, as she has been seeing the married dragoon, Count Carl-Magnus Malcolm. Upon learning that Fredrik has gone for eleven months without sex, she agrees to accommodate him as a favor for an old friend.
Madam Armfeldt offers advice to young Fredrika. The elderly woman reflects poignantly on her own checkered past, and wonders what happened to her refined “Liaisons”. Back in Desiree’s apartment, Count Carl-Magnus Malcolm proclaims his unannounced arrival in his usual booming tones. Fredrik and Desiree fob off the Count with an innocent explanation for their disheveled appearance, but he is still suspicious. He instantly dislikes Fredrik and returns to his wife, Countess Charlotte. Charlotte knows of her husband’s infidelity, but Carl-Magnus is too absorbed in his suspicions of Desiree to talk to her (“In Praise of Women”). When she persuades him to blurt out the whole story, a twist is revealed—Charlotte’s little sister is a schoolfriend of Anne’s.
Charlotte visits Anne and describes Fredrik’s tryst with Desiree. Anne is shocked and saddened, but Charlotte explains that such is the lot of a wife, and love brings pain (“Every Day a Little Death”). Meanwhile, Desiree asks Madam Armfeldt to host a party for Fredrik, Anne and Henrik. Madam Armfeldt reluctantly agrees, and sends out a personal invitation; its receipt sends Anne into a frenzy, imagining “A Weekend in the Country” with the Armfeldts. Anne does not want to accept the invitation, but Charlotte convinces her to do so to heighten the contrast between the older woman and the young and beautiful teenager. Charlotte relates this to the Count, who (much to her chagrin) decides to visit the Armfeldts uninvited. Carl-Magnus plans to challenge Fredrik to a duel, while Charlotte hopes to seduce the lawyer to make her husband jealous and end his philandering. The act ends as all characters head to Madam Armfeldt’s estate.
Madam Armfeldt’s country estate is bathed in the golden glow of perpetual summer sunset at this high latitude (“Night Waltz One and Two”). Everyone arrives, each with their own amorous purposes and desires—even Petra, who catches the eye of Armfeldt’s fetching manservant, Frid. The women begin to quarrel with one another. Fredrik is astonished to learn the name of Desiree’s daughter. Henrik meets Fredrika, and confesses to her he deeply loves Anne. Meanwhile, in the garden, Fredrik and Carl-Magnus reflect on the difficulty of being annoyed with Desiree, agreeing “It Would Have Been Wonderful” had she not been quite so wonderful. Dinner is served, and the characters’ “Perpetual Anticipation” enlivens the meal.
At dinner, Charlotte attempts to flirt with Fredrik, and trades insults with Desiree. Soon, everyone is shouting and scolding everyone else, except for Henrik, who finally speaks up. He accuses the whole company of being amoral, and flees the scene. Stunned, everyone reflects on the situation and wanders away. Fredrika tells Anne of Henrik’s secret love, and the two dash off searching for him. Meanwhile, Desiree meets Fredrik and asks if he still wants to be “rescued” from his life. Fredrik answers honestly that he loves Desiree, but cannot bring himself to part with Anne. Hurt and bitter, Desiree can only reflect on the nature of her life and relationship to Fredrik (“Send In the Clowns“). Anne finds Henrik, who is attempting to commit suicide. The clumsy boy cannot complete the task, and Anne tells him that she loves him, too. The pair begins to kiss, which leads to Anne’s first sexual encounter. Meanwhile, not far away, Frid sleeps in Petra’s lap. The maid imagines advantageous marriages, but concludes that in the meantime, “a girl ought to celebrate what passes by” (“The Miller’s Son”). Charlotte confesses her plan to Fredrik, and both watch Henrik and Anne, happy together, run away to start their new life. The two commiserate on a bench. Carl-Magnus, preparing to romance Desiree, sees this and challenges Fredrik to Russian Roulette; Fredrik nervously misfires and simply grazes his own ear. Victorious, Carl-Magnus begins romancing Charlotte, finally granting her wish.
After the Count and Countess leave, Fredrika and Madam Armfeldt discuss the recent chaotic turns-of-events. The elderly woman then asks Fredrika a surprising question: “What is it all for?” Fredrika thinks about this, and decides that love, for all of its frustrations, “must be worth it”. Madam Armfeldt is surprised, ruefully noting that she rejected love for material wealth at Fredrika’s age. She praises her granddaughter and remembers true love’s fleeting nature.
Fredrik finally confesses his love for Desiree, acknowledging that Fredrika is his daughter, and the two promise to start a new life together (“Send in the Clowns” (Reprise)). Madam Armfeldt sits alone with Fredrika, who tells her grandmother that she has watched carefully, but still has not seen the night smile. Madam Armfeldt laughs and points out that the night has indeed smiled twice: first on Henrik and Anne, the young, and second on Desiree and Fredrik, the fools. As the two wait for the “third smile… on the old”, it occurs: Madam Armfeldt closes her eyes, and dies peacefully with Fredrika beside her.