George Bailey is going to kill himself.
Or, at least, he's toying with the idea. Fortunately, the prayers of his friends and family inspire some divine intervention: two senior angels commission one of their apprentices, Clarence, to save the despondent George. To bring him up to speed, they show Clarence (and us) some of the highlights of George's life, with some freeze-frames for angelic editorial comments. Clarence is pumped. If he can help George, maybe he can finally get his wings. He's been a little insecure about it.
Angel Joseph starts at the beginning, showing Clarence a young, gregarious, energetic George who's already got big plans to explore the world and do great things. We watch him save his younger brother Harry's life after he falls into an icy pond, in the process losing the hearing in one ear from pneumonia. We watch him avert disaster when he prevents the drugstore owner he works for from accidentally giving poison to a sick child. He grows up to be a selfless, popular young man … who looks exactly like Jimmy Stewart.
After four years helping his father run his Building and Loan business after graduation, George is ready to leave for Europe and pursue those dreams of travel and college. His dad's death dashes those dreams. (Like that alliteration? Thanks.) Like the good guy he is, he stays in Bedford Falls to keep the family business out of the hands of the town's rich and nasty tycoon, Henry Potter—not to be mistaken for Harry. He uses his college savings to send Harry to school instead.
When Harry graduates, George can finally turn over the business to him and set out on his travels and education. But, Harry has been offered a great job with his new father-in-law, and it's out of town. George doesn't have it in his heart to make him stay. Dream postponed again.
One upside to being stuck in Bedford Falls is that he falls head over heels for local beauty Mary Hatch and makes her Mrs. George Bailey. He's saved up $2,000 for a honeymoon in Bermuda. Finally, he'll get to—
Not so fast.
On the way to the train after their wedding, he and Mary notice people clamoring to get into the bank. The evil Mr. Potter has called back their loans, and the people are panicked—they want to withdraw their money. But, the Building and Loan doesn't have much cash on hand. Where could it possibly come from? You guessed it: George and Mary's honeymoon stash.
Clarence's angel bosses show him how George keeps on keepin' on. Despite his happy life with Mary and their kids, George still feels like he hasn't realized his potential. He's never seen the world; his best buddy strikes it rich in plastics, while George is scraping by; his brother's a Navy war hero who saves a ship full of serviceman, while George can't enlist because of his hearing loss.
One day, Uncle Billy accidentally misplaces $8,000 of their customers' money—a ton of money in the 1940s, over $100,000 today. Mr. Potter finds it, keeps it, and frames George for stealing his borrowers' money. Totally distraught, thinking he's facing scandal and prison, George snaps at his wife and kids, trashes the house, crashes his car into a tree, and stares into an icy river, contemplating suicide. But, someone else falls in the river at that very moment, and George jumps in to rescue him.
Turns out, the guy who fell in the river was Clarence, George's guardian angel-in-training. He knew George would jump in after him. A skeptical George tells Clarence it would be better if he'd never been born. Inspired, Clarence decides to perform a miracle and show George what the world really would be like if he'd never lived. It's a life retrospective, minus George's life.
We see that without George around, Harry drowned in the icy pond as a kid, and all the men he saved in the war are dead, too. The drugstore owner accidentally poisoned a child. And, without George to stop him, Mr. Potter has transformed the town into a hedonistic den of iniquity devoid of the small-town values that formerly sustained it.
George meets his mother, who's grieving for Harry, her only son. She's running a boarding house now and doesn't even recognize George. He encounters Mary, now an unmarried librarian (horrors), who screams when he pleads with her to recognize him. Violet has become a prostitute.
Realizing that his life was pretty meaningful and wonderful after all, George wants to live again. He clicks his ruby slippers three times and says, "There's no place like home." (Well, he could have.) He joyfully runs home, where everyone recognizes him again and the grateful townspeople have raised more than enough money to bail out the Building and Loan. As George holds his daughter Zuzu, a bell on the Christmas tree rings. Zuzu says her teacher told her that "every time a bell rings, an angel gets its wings." George smiles.
Way to go, Clarence.