The villagers are coming in from a long, hot day. They enjoy hearing Adina read from the story of Tristan and Isolde and the magic love potion. Nemorino watches from a distance, yearning for even a word from Adina. He approaches her afterwards and professes his love. She shoos him away with brisk (and beautiful) words about the need for fickleness.

The army is in town. Sergeant Belcore enters, intent on storming the heart of Adina, the most beautiful and successful girl in town. She seems impressed. Nemorino is full of disgust and despair.

A cart pulls up carrying the Great Doctor Dulcamara, bearing pills and potions for every kind of ailment. He is most proud of his cure-all elixir. Nemorino approaches him quietly and asks whether he possesses the love potion of Queen Isolde. Absolutely, Dulcamara assures him. He will have damsels fawning over him. But he must wait a day for it to work. (Dulcamara has never heard of Isolde, the potion is a cheap Bordeaux, and the time would allow the Doctor to leave town.) He downs the flask and immediately feels robust enough to ignore Adina the next time he sees her. To get even, she consents to marry Belcore. Nemorino, horrified, begs her to wait another day.

Everyone is assembled for the wedding of Adina and the sergeant. Adina privately murmurs that she’s waiting to sign the marriage contract until Nemorino arrives. Nemorino seeks out the doctor to ask for another bottle of the elixir. Dulcamara agrees to wait until he can borrow the money. Belcore strides by, puzzled by Adina’s postponement. Nemorino laments that he is penniless. Belcore suggests he join the army and receive the volunteer bonus. Nemorino, jubilant, signs, and takes the cash back to Dulcamara for another bottle.

Suddenly the village girls surround Nemorino. He thinks this is the effect of the elixir; he does not yet know that his uncle has died and left him a fortune. Adina has felt responsible for his enlistment, but her guilty feeling turns to jealousy and sadness when she sees him with all the girls. Dulcamara offers her the elixir, but she assures him she can win Nemorino back on her own.

Nemorino was by no means indifferent: during all the confusion he noticed a tear upon Adina’s cheek. He is sure she cares for him. Adina approaches Nemorino and shows him that she has bought back his military contract. He feigns indifference, and she finally confesses her love. Belcore struts by, finds them together, and consoles himself by proclaiming that the world is full of women for him. Dulcamara redoubles his boasting: the magical elixir can make poor men into millionaires and can bring true love.