Lights, camera, action!
Because this movie revolves around a long weekend (bet you figured that one out), The Lost Weekend can be easily broken down into a day-by-day format.
Day One
Don and Wick Birnam are packing their bags for a weekend getaway. Don's a recovering alcoholic, and has hidden a bottle of whiskey on a rope outside his window, which he's desperately trying to get access to. His girlfriend Helen arrives and Don convinces Wick to go to a show with her so he can get some much-needed alone time with his whiskey. Unfortunately for him, Wick discovers the booze before he leaves…but goes to the show anyway. (Wick's fed up with Don's shenanigans.)
After trying and failing to locate another hidden stash, Don steals the cleaning lady's paycheck—what a jerk—and buys two bottles of rye whiskey. He then proceeds to get so plastered at Nat's Bar that he misses his train to the country, but he arrives in time to see Wick leave.
Helen has decided to wait in front of the building for Don to come home, so he sneaks past her so he can binge-drink in peace. He hides one bottle in a light fixture before drinking the other and passing out.
This guy is a mess.
Day Two
Don had gotten so drunk that he forgot about his second bottle, so he heads to Nat's Bar first thing in the morning. Nat reminds him, but Don hangs and kicks back some shots anyway.
We then go into Flashback Land as Don tells Nat about his relationship with Helen. They'd met by chance three years prior after their coats got mixed up at an opera and have been together since. She didn't discover that he was an alcoholic for a while, but she's been steadfast in her support since then. We also learn that Don's addiction was born out of his failed ambitions as a novelist. (Whoa: a drunk writer? That's not stereotypical.)
Don makes a date he has no intention of keeping with a girl named Gloria and returns home to work on his novel, The Bottle. Cue writer's block. After tearing apart his apartment in search of his hidden stash (no luck), Don goes to a fancy bar and steals a woman's purse…though he gets caught and thrown out.
Upon returning home, however, he promptly discovers his stashed bottle and gets shmammered.
Day Three
Don is now out of booze and—even worse—broke. He grabs his typewriter and tries to sell it at nearby pawnshops, but they're all closed on account of the Jewish holiday of Yom Kippur.
Desperate, Don stumbles across Gloria's apartment and cons her into giving him some money. As he descends her stairs, however, he trips and falls, taking a nasty splat on her hard tile floor. Drunkenness and stairs don't mix, kids.
Day Four
To his surprise, Don wakes up in an alcoholic ward—he'd been brought there after his accident—where a creepy nurse named Bim warns him against the futility of fighting addiction.
That night, he sees a man having a hallucination caused by alcohol withdrawal (known as the DTs) and escapes under the cover of night. We don't blame him for being freaked out.
Day Five
Don waits outside a liquor store until it opens and intimidates its owner into giving him a bottle of whiskey. After returning home and consuming half of the bottle, Don experiences a DT-induced hallucination himself: a bat attacking and killing a small mouse. He screams bloody murder.
Hearing this, his landlady contacts Helen, who rushes over. Helen tells Don that it was all imaginary and calms him down before they go to sleep.
Day Six
The next morning, Helen's awoken by Don rushing out of the apartment with her coat. He's going to sell it at a pawn shop. To Helen's surprise, however, he doesn't sell it for booze money—he trades it for a gun. Realizing that Don is planning to kill himself, Helen tries to distract him by any means necessary, even offering him booze.
Don quickly realizes what's up and grabs the gun before Helen does. Before he can do anything with it, however, Nat arrives with Don's typewriter in hand—he'd picked it up after Don's fall.
Suddenly, Don's struck by the realization that he can escape his addiction through writing—and that his novel The Bottle can help others battling the bottle.