In 1923, college freshman Harold Diddlebock (Harold Lloyd) is brought into his college's football team where he scores the winning touchdown for his team (as told in 'The Freshman'). The mild-mannered Harold Diddlebock is promptly hired by the pompous New York advertising tycoon J.E. Waggleberry (Raymond Walburn) to work at his firm. Harold is given a low-paying job at the firm's bookeeper.
Jumping forward 22 years to 1945, Harold (still working in his boring job as bookkeeper) is promptly let go by Waggleberry with nothing but a tiny pension of around $1,000. Harold bids farewell to the girl at the desk down the aisle, Miss Otis (Frances Ramsden), whom he had hoped to marry just as he had hoped to marry five of her older sisters before whom also worked at the firm.
As Harold wanders aimlessly through the streets, his life's savings in hand, he has a run-in with an older man; a slimy racetrack tout and con-artist named Wormy (Jimmy Conlin). Seeing the large amount of cash that Harold has on him, Wormy takes Harold to a nearby bar for a drink (hoping that Harold will get drunk enough to lend him some of his money). When Harold tells the bartender (Edgar Kennedy) that he's never had a drink in his life, the barkeep creates a potent cocktail he calls "The Diddlebock", one sip of which is enough to release Harold from all his inhibitions, setting him off on a day-and-a-half binge of spending and carousing. Harold then goes to a tailor and barber shop and spends most of his money and bets the rest on a horse race and wins.
Some days later, Harold wakes up on the couch in the house of his widowed older sister Flora (Margaret Hamilton). He finds that he has a hangover, but he also has a garish new wardrobe, a ten-gallon hat, a hansom horse-drawn cab complete with a driver, and ownership of a bankrupt circus.
Trying to sell the circus, Harold and Wormy visit the circus-loving Wall Street banker Lynn Sargent (Rudy Vallee), and then, when he turns them down, so do the rest of the town's bankers. To get past the bank guards, Harold brings along Jackie the Lion, who incites panic. Wormy brings along a thermas containing the potent 'Diddlebock' drink where they give shots to each of the bankers to get them inhebriated to sign over. However, things take a turn when Harold, Wormy and the lion end up on the ledge of a skyscraper after the lion gets loose. But they avoid plunging to certain death.
The three are arrested and thrown in jail, but Miss Otis bails them out, and they find that the publicity has attracted a mob of bankers who want to buy the circus but Ringling Brothers outbids them. Harold celebrates with another "Diddlebock".
In the final scene, Harold wakes up another day or two later in the horse-drawn carriage with Miss Otis where he finds out that he got $175,000 for the circus, he's now an executive at Waggleberry's agency, and that he and Miss Otis got married during his last binge.