Let's start at the very beginning (a very good place to start). As you read through the summary, just picture people busting out into song every few minutes. Believe us, it's more fun that way.
The camera soars over the Austrian Alps. There's a woman happily twirling and singing. It's Mary Poppins.
Oops, our mistake. Not Mary Poppins. Let's rewind.
The twirling and singing woman is Maria, a young woman studying to become a nun in an abbey in Salzburg. Unfortunately, her general zest for life is getting in the way of her spiritual duties, so the Reverend Mother (head honcho of the abbey) suggests that she try something else for a while. Her plan: send Maria to live with widower Georg von Trapp, a navy captain who desperately needs help with his seven children. Since his wife's death, the cap'n runs his house like a ship, calling the children with a ship's whistle and insisting on absolute order and control.
No. Fun. Allowed.
The kids don't make things easy for Maria at first. They've managed to send dozens of governesses packing with their pranks and misbehavior. But that night, a thunderstorm drives them all into Maria's room; the children realize that Maria is buckets of fun and very motherly. The captain goes away to Vienna, and the kids and Maria end up running around Salzburg singing, dancing, climbing trees, and just generally having the kind of fun that their super-stern dad doesn't permit.
Coming home from Vienna to find the kids and Maria soaking wet and having absolutely too much fun after a boating adventure, the captain fires her. Enter the sound of music to save the day: he overhears the children singing a song that Maria's taught them and he's overwhelmed with emotion. He's not an ice-cold creep after all; he used to sing all the time before his wife died. He tells Maria she's brought joy back to the house and begs her to stay.
The captain lightens up and gets closer to his children. There's a minor complication at this point, though: Maria and the captain develop feelings for each other although neither of them really know it yet. And the captain's already dating the lovely and sophisticated Baroness Schraeder.
The baroness tries to remove the third side of the love triangle by making Maria aware of the captain's feelings for her, which mortifies Maria and sends her fleeing back to the abbey without so much as a goodbye to the children. The captain and the baroness get engaged. The kids are not all right.
After the children show up at the abbey looking for their gone governess, the Reverend Mother susses out what's happened and sends Maria back to the von Trapps. She won't let Maria run away from her feelings. Maria thinks she's off the hook when she learns that the captain and the baroness are engaged, but the baroness breaks off the engagement pretty soon after Maria's return. She's no dummy; she sees how the captain is feeling about Maria. With the baroness out of the way, Maria and Georg confess their love and get hitched.
The captain and Maria return from their honeymoon to find that Germany has annexed Austria. We hate when that happens. There's a telegram demanding that Captain von Trapp take a post with the German navy and hang Nazi flags in his house. Since Georg hates the Nazis and the occupation, he decides that he and the family need to get out of the country ASAP.
Their plan hits a snag when Nazi Party leader Herr Zeller catches them on their way out of town. They convince Zeller that they're just on their way to sing in a folk festival that's going on that night. He's suspicious, but lets them go as long as he escorts them there. He believes that allowing them to sing will show the Austrian audience that life in their country goes on as usual. See? The Nazis are warm and fuzzy music lovers.
The Von Trapp Family Singers are crushing it at the Festival. But just before the awards presentation, they sneak out; the nuns hide them in the abbey. After a near-catastrophe with the Nazis, they jump in their car, head to the Swiss border, and begin their climb through the Alps to freedom.
And that's that. So long, farewell, auf Wiedersehen, goodnight.