A group of young Bohemians – poet Rodolfo, artist Marcello, philosopher Colline and musician Schaunard – are struggling to keep warm in the freezing cold of their Parisian garret. They try to heat up the room, but cannot get a good fire burning in the stove. Schaunard arrives bearing food and firewood, having had a stroke of luck working for a wealthy client, but suggests that they go out to eat in the Latin Quarter, since it’s Christmas Eve. When their landlord Benoît knocks at the door and demands the rent, they invite him in for a drink before throwing him out in feigned disgust at his carrying on with other women behind his wife’s back. After this, Marcello, Colline and Schaunard set out for the Café Momus, while Rodolfo stays behind to finish the article he’s writing before joining them. He hears another knock at the door – this time it’s their neighbour, Mimì, whose candle has gone out. Very pale, she faints; having come round, she realises she has dropped her key. As the two of them feel around for it in the darkness, Rodolfo finds it but hides it in his pocket to prolong the physical closeness between them. Struck by an irresistible mutual attraction, they tell each other something about themselves (Mimì, a seamstress, embroiders flowers for a living), before deciding to go and meet his friends at the Café Momus.

The streets of the Latin Quarter are bustling with life. Street vendors call out their wares and Rodolfo buys Mimì a bonnet from one of the shops. They join the others at a table outside the café. Before long, Musetta arrives – an attractive young woman, she is accompanied by Alcindoro, a pompous and elderly admirer. Marcello, her former lover, does his best to ignore her, but she is determined to capture his attention by whatever means necessary. With her seductive charms and a dash of cunning, she eventually succeeds – having got rid of Alcindoro by pretending one of her shoes is too tight and sending him off to buy her a new pair, she falls into the arms of a joyful Marcello. She tells the waiter Alcindoro will pay both bills when he comes back and the six of them depart in high spirits.

On a cold February day, Mimì comes to an inn near one of the customs gates in Paris, where Marcello and Musetta are now living. Marcello tells Mimì that Rodolfo is inside, but she refuses to go in, confiding in him that the poet’s jealousy is ruining their relationship. She thinks – and Marcello agrees – that the best thing for them would be to go their separate ways. When Rodolfo comes out, Mimì hides, and then overhears him telling his friend that her illness is getting worse and worse, and that he can’t bear not having the means to look after her. When her presence is discovered, Mimì is reunited with Rodolfo. As Marcello goes to see who Musetta is flirting with now, having heard her laughing inside, the other two prepare to say their goodbyes, but ultimately decide to stay together until spring. Meanwhile, Musetta and Marcello fling insults at one another, having launched into another of their interminable arguments.

Back in the garret of Act One, Rodolfo, who has now parted company with Mimì, is trying to write and Marcello to paint, but both men are distracted by thoughts of the women they love. Schaunard and Colline come back with some meagre provisions, at which they all act as if they’re about to have a great feast and start suggesting a variety of dances they could perform. Suddenly Musetta appears and tells them that Mimì is on the staircase, but too ill to climb all the way to the garret. Musetta had met her wandering the streets, her only desire to return to the garret and die close to Rodolfo. They carry her in and lay her on the bed. While the others go off to sell what they can to buy medicine for her, Mimì and Rodolfo reminisce about their first meeting and the happy times they spent together after that. Their friends return with medicine and a muff to warm Mimì’s hands, but it is too late. After saying a few words of thanks to them, she dies, leaving Rodolfo griefstricken.