The action takes place in Wetzlar, near Frankfurt am Main, in about 1780
In the garden of his house, the Bailiff is teaching his young children a Christmas carol. Enter Schmidt and Johann, friends with whom he plays cards quite often. His friends tease him for beginning Christmas carol rehearsals in July. Then they greet Sophie, the Bailiff’s second eldest daughter, and ask where her elder sister Charlotte is. Sophie explains that Charlotte’s getting ready to go to the local ball that evening. Schmidt and Johann discuss several of the young men who’ll be at the ball—amongst them youthful Werther who, according to Charlotte’s father, has a promising future. Schmidt, however, comments on his melancholy disposition. He then asks after Albert, Charlotte’s fiancé, who’s been out of town on business for several months. The Bailiff explains that he’s had no news of him for days. Johann and Schmidt go on ahead to the tavern, to await the Bailiff there, while he takes his leave of his children. Several guests arrive, having arranged to meet at Charlotte’s house so that they can go to the ball together. Amongst them is Werther, who stands by the fountain on the patio rhapsodizing about the natural beauty of the spot. Charlotte bids her father a fond farewell and asks her sister Sophie to look after their littlest siblings while she’s at the ball. The Bailiff greets Werther and introduces him to his daughter. The youth is entranced by Charlotte’s beauty. The young folk go off to the ball while the Bailiff goes to join his friends at the tavern.
After they’ve all gone, Charlotte’s fiancé Albert arrives at the house; he hadn’t told her he was coming home because he wanted to surprise her. Albert is disappointed at finding only Sophie at home. However, he soon brightens up when she talks about Charlotte’s love for him and the preparations they’ve been making for their wedding. Albert takes his leave and Sophie goes back into the house to look after her siblings. Romance is in the air between Charlotte and Werther when they return, but her father’s news that Albert’s back brings them down to earth again. Charlotte explains to Werther that she gave her word to her dying mother that she’d marry Albert. Werther, irresistibly drawn to Charlotte, is thrown into dismay.
In a public square. Three months have passed since Albert and Charlotte were married, and they’re on their way to the church, where the pastor’s golden wedding anniversary is being celebrated. Werther trails after them disconsolately. Albert goes to comfort him, saying he understands the depth of his feelings for Charlotte. Sophie comes up, wanting Werther to take her to the ball that’s been arranged for the pastor’s anniversary; she’s secretly in love with Werther—but he can’t get Charlotte out of his mind, and as soon as he spies an opportunity, he goes up to her to declare his love for her again. She tells him it cannot be, and gives him the brush-off. She suggests to Werther that he spends some time out of town and doesn’t return before Christmas. Sophie reappears and pesters Werther to take her to the ball; he turns her down again, and she weeps in desperation. Her sister Charlotte comes over to comfort her.
In Albert and Charlotte’s home. It’s Christmas Eve. Unable to get Werther out of her mind, Charlotte re-reads the letters in which he declares his impossible love to her again and again. She admits to herself that she loves him too. Sophie arrives bearing Christmas presents for the youngest siblings. When Sophie enquires after Werther, Charlotte, her heart torn in two, breaks down and cries. As Sophie leaves she invites Charlotte to come over to their father’s house to hear their siblings singing the carols he taught them. A haggard Werther unexpectedly appears. Here he is, he says, obeying Charlotte’s expressed wish that he return at Christmas, even though he himself had wished he were dead. Werther reads out part of an Ossian poem, and Charlotte is visibly moved. She weakens and they embrace; then she pushes him away again. Werther leaves the house bereft of all hope. Albert arrives home to find his wife in a troubled state. A note from Werther himself is handed to Albert, asking to borrow his pistols because he’s "going on a long journey". Charlotte, reading between the lines, hurries off to try to prevent Werther’s suicide.
The snow-covered landscape reflects the moonlight, appearing as bright as day. Charlotte arrives at Werther’s home to find him fatally wounded. The youth asks Charlotte to forgive him, but she feels that she’s to blame for his suicide. Charlotte holds him in her arms as he breathes his last words. In the distance the children can be heard singing carols as Werther dies in his sweetheart’s arms.