Sabrina Fairchild (which is a totally apt name: she's young and super-pretty) is the young daughter of Thomas, the chauffeur on the Long Island estate of the wealthy Larrabee brothers.
Sabrina's in love with the younger Larrabee brother, the irresponsible playboy David, but he doesn't know she exists. Of course, this is extremely unlikely since Sabrina is played by Audrey Hepburn, and no matter how rich you are, you're going to notice that one of the most beautiful women in the world is living above your garage.
But this is fantasy, so you just have to suspend your disbelief for a little bit.
Sabrina is filled with grief because David ignores her while flirting (and probably more than flirting) with another woman. So on the night of a party, before she's to go to Paris, she tries to kill herself with carbon monoxide poisoning in the garage. Whoa, Sabrina. That's a little extreme. Older brother Linus Larrabee finds her and rescues her.
Do we smell foreshadowing, or are those fumes getting to our head?
The next day she's shipped off to Paris, where she attends cooking school and meets Baron St. Fontanel—who does notice that she's one of the most beautiful women in the world, and takes her under his wing. She cuts her hair, buys new clothes, and learns to embrace love and life… because that's what you do in Paris.
Meanwhile, back in the good ol' US of A, Linus has arranged a marriage for David with socialite Elizabeth Tyson, whose family has a sugar-cane fortune. Linus is going to use sugarcane in his new cutting-edge plastic. David doesn't really want to marry Elizabeth, but Linus bullies David into it.
Plot point: Linus is really a controlling jerk.
Sabrina comes back home, and hey, suddenly David notices that she's one of the most beautiful women in the world. He doesn't even recognize her at first, but that doesn't stop him from inviting her to a party at the main house. He's in love, she's in love—but Linus doesn't like it, because he wants David to marry Elizabeth so he can make beautiful plastic. He tricks David into sitting on some wine glasses, badly injuring his butt. Then he decides to court Sabrina himself and make her fall in love with him.
You might not think that would work so well because Linus is three decades older than Sabrina, and significantly less good-looking than David. But the script says it works, so it works; after they go out for several evenings, Sabrina starts to fall for Linus.
But—plot twist—Linus also starts to fall for Sabrina, to the irritation of Sabrina's father, the chauffeur, who fears Sabrina will be hurt. Smart dad.
Sabrina urges Linus to go to Paris because Paris will fill him with life and make him stop being such a fuddy-duddy. Linus hints that he would like to go there with Sabrina. Happiness in reach? Yes.
Linus can't quite admit to himself he loves Sabrina. So, like any logical person would do, he plans to book them on a boat to Paris, and then not show up. But then he tells Sabrina he's not going to show up, ruining the whole plan. (Ruining plans like that is what you do when you're in love.) Sabrina is angry, but she takes the ticket to Paris anyway, showing that she has good sound business sense. No wonder Linus likes her.
Linus thinks Sabrina and a finally-healed David have gone to Paris together, so he calls a board meeting to tell Elizabeth Tyson that the marriage is off and the plastics deal is off and everything is off. But then David (surprise, not in Paris) shows up to say the marriage is still a go and that Linus is in love with Sabrina and should scurry off to catch the boat to Paris.
Linus realizes he loves Sabrina, and catches her on the boat, where they embrace.
Though… David is still marrying Elizabeth, even though he doesn't love her, or even really like her. So there's a good chance they're going to be miserable. But oh well: that's what they get for not being the stars of the picture.