Seville at dawn. Fiorello quietly leads on a merry band of musicians, all of them hired by the Count Almaviva, with the express purpose of serenading the lovely Rosina. The Count appears, and sings a beautiful air to lure her to the window, but she fails to appear. Almaviva pays off the musicians, and, in their joy at being musicians being paid, they exit noisily. The local do-it-all, Figaro, arrives into the scene proclaiming his prowess with his many skills. Though the Count is traveling in disguise as the poor student Lindoro (with the goal of wooing fair Rosina), Figaro recognizes his old friend. Almaviva informs Figaro that he wishes to remain incognito. Figaro tells Almaviva that Rosina is, in fact, the ward of the old Dr. Bartolo, who intends on marrying her and keeping her for himself. Bartolo appears, and securely locks the doors to his house. With the prompting of the promise of renumeration from the Count, Figaro hatches a plan: Almaviva will enter the house as a drunken soldier and insist on being billeted there.
Rosina has written a letter to the mysterious admirer who serenades her from outside her window. She reminds us that while she may be sweet, when her ire is aroused, she becomes a viper. Figaro enters with Dr. Bartolo, and is promptly followed by the music master, Don Basilio. Basilio has heard that Count Almaviva, enchanted by Rosina’s beauty, has come to Seville to pursue her hand. To thwart this, Basilio proposes to Bartolo that they spread vicious rumors around Seville, to give him the appearance of a cad, thus squelching any romantic notions growing in Rosina’s heart. Bartolo, nervous at the prospect of losing Rosina, goes off with Basilio to draft a marriage contract for a wedding that day. Figaro overhears this, and warns Rosina. Rosina is confident that she can deal with Bartolo, and wants to know just who is the young man she has seen with Figaro. He says it is his poor cousin Lindoro, and then tells her to write a letter to him. She produces one already written, giving it to Figaro to deliver. Bartolo reappears, seems to confirm his suspicions that something is up when he examines Rosina’s ink-stained fingers, and threatens to lock her up for good.
Almaviva, now disguised as a drunken soldier, arrives and bangs on the door, insisting that he be put up in Bartolo’s house. Bartolo tells the impertinent young soldier that he is, in fact, exempt from housing him, and searches for the document that says so. Almaviva lets Rosina know that he is Lindoro, and passes a note proclaiming his love for her. Bartolo, seeing this, demands to know what piece of paper is in her hands; the ever-resourceful Rosina manages to switch the love note for a laundry list. Figaro arrives, alerting everyone that the melee can be heard throughout the entire neighborhood. Berta and Don Basilio enter to see what’s going on, and Berta nearly faints at the prospect of a drunk young soldier staying in the house. Soldiers arrive, demanding to know what all the fuss is about. Bartolo insists that they arrest Almaviva / Lindoro / Soldier for drunkenness, but they quietly back down when Almaviva quietly shows them a document revealing his true identity. All is general chaos and confusion, and in a brilliant concerted finale, the parties involved tell the audience this.
It is time for Rosina’s music lesson; today, Basilio is ill, and she has a substitute teacher, Don Alonso, who is none other than that handsome Lindoro in yet another disguise. “Don Alonso” gives Bartolo Rosina’s love note, proving that she is faithless. He then quietly lets on to Rosina that he is Lindoro in disguise, and the two of them manage to flirt back and forth all under the watchful, if unobservant, eye of Dr. Bartolo. She sings an aria from the new opera The Useless Precaution, and Bartolo dozes off as Lindoro coaches her. He suddenly wakes and irked by this “contemporary music”, preferring old chestnuts from his era. Unluckily for everyone, he demonstrates. Figaro arrives to give Bartolo his shave, and craftily manages to get the keys to Rosina’s balcony door. To everyone’s amazement, Basilio arrives to give Rosina her lesson, looking a little too healthy. Figaro pays him off, and manage to convince him (and, importantly, Bartolo) that he has scarlet fever and needs to head straight to bed. As Figaro resumes shaving Bartolo, Almaviva and Rosina make a plan to escape together at the stroke of midnight. Bartolo overhears this, and becomes enraged and forces everyone out. Berta comes in to clean up the room, and muses on foolish old men who pursue much younger women.
Outside the house, Bartolo runs into Basilio, and insists that Basilio quickly get a notary to the scene. He then shows Rosina the letter she had written to Lindoro, tells her that it was given to him by Count Almaviva, and urges her to marry him at once. Convinced of Lindoro’s betrayal (he must be working for that lecherous Count), she reluctantly agrees. The heavens disagree, and whip up a noisy tempest.
Figaro and Almaviva enter the house through Rosina’s balcony, intending to free Rosina. However, she wants nothing to do with them, accusing “Lindoro” of intending to pass her to the Count for his own interests. Finally, Almaviva casts off his disguises, and tells her who he really is. She is overjoyed, and the two sing of their love for each other, all while Figaro urges them to escape while they can. They go on a bit too long, and the ladder to Rosina’s balcony disappears. Basilio and the notary enter, and Figaro, seizing the opportunity, has the notary marry Almaviva and Rosina at once. Bartolo arrives with the soldiers, only to find that his Rosina is now married to another. He is slightly pacified by the fact that he gets to keep her dowry, and ultimately blesses the couple.