In the salon of “the richest man in Vienna,” preparations are in progress for a new opera seria based on the Ariadne legend, with which the master of the house will divert his guests after a sumptuous dinner. The Music Master, having heard that a foolish comedy is to follow his pupil’s opera, accosts the pompous Major-domo and warns that the Composer will never tolerate such an agreement. The Major-domo is unimpressed. No sooner have they gone than the young Composer comes in for a final rehearsal but an impudent lackey informs him that the violins are playing at dinner. A sudden inspiration brings him a new melody, but the Tenor is too busy arguing with the Wigmaker to listen to it. Zerbinetta, pert leader of some comedians, emerges from her dressing room with an Officer just as the Prima Donna comes out asking the Music Master to send for her protector, “the Count.” At first attracted to Zerbinetta, the Composer is outraged when he learns she and her troupe are to share the bill with his masterpiece. Zerbinetta and the Prima Donna lock horns while dissension spreads. As the commotion reaches its height, the Major-domo returns with a flourish to announce that because of limited time, the opera and the comedy are to be played simultaneously, succeeded by a fireworks display. At first dumbstruck, the artists try to collect themselves and plan: the Dancing Master extracts musical cuts from the despairing Composer, with the lead singers each urging that the other’s part be abridged, while the comedians are given a briefing on the opera’s plot. Ariadne, they learn, after being abandoned by Theseus, has come to Naxos to wait for death. “No,” says Zerbinetta – she only needs a new lover. The comedienne decides her troupe will portray a band of travelers trapped on the island by chance. Bidding the Composer take heart, she assures him that she, like Ariadne, longs for a lasting romance, but as his interest in the actress grows, she suddenly dashes off to join her colleagues. Now the Prima Donna threatens not to go on, but the Music Master soothes her by promising a triumph, and the heartened Composer greets his teacher with a paean to music. At the last minute he catches sight of the comics in full cry and runs out in horror

Ariadne is seen in her grotto, watched over by three nymphs – Najade, Dryade, and Echo – who sympathize with her grief. Enter the buffoons, who attempt to cheer her up, to no avail. As if in a trance, Ariadne resolves to await Hermes, the messenger who will take her to another world, undefiled – the realm of death. When the comedians still fail to divert Ariadne, Zerbinetta addresses her directly, describing the frailty of women, the willfulness of men, and the human compulsion to change an old love for a new. Insulted, Ariadne retires to her cave, and when Zerbinetta concludes, her cronies leap on for more sport. Harlequin tries to embrace her while Scaramuccio, Truffaldino, and Brighella compete for her attention, but it is Harlequin to whom she at last surrenders. The nymphs return, heralding the approach of a ship. It bears the young god Bacchus who has escaped the enchantress Circe (unchaste love) for Ariadne (purity). Bacchus is heard in the distance, and Ariadne prepares to greet her visitor – surely Death at last. When he appears, she at first thinks Theseus has come back to her, but he majestically proclaims his godhood. Entranced by her, he claims he would sooner see the stars vanish than give her up. Reconciled to a new, exalted existence, Ariadne joins Bacchus in an ascent to the heavens as Zerbinetta sneaks in to have the last word: “When the newest god approaches, we surrender, we are his.”