A chemist finds his personal and professional life turned upside down when one of his chimpanzees finds the fountain of youth.
Barnaby Fulton is a research chemist working on a fountain of youth pill for a chemical company. While trying a sample dose on himself, he accidentally gets a dose of a mixture added to the water cooler and believes that his potion is what is working. The mixture temporarily causes him to feel and act like a teenager, including correcting his vision. When his wife gets an even larger dose, she regresses even further into her childhood. When an old boyfriend meets her in this state, he believes that her never wanting to see him again means a divorce and a chance for him.—John Vogel <[email protected]>
Dr. Barnaby Fulton (Cary Grant), an absent-minded research chemist for the Oxley chemical company, is trying to develop an elixir of youth. His wife, Edwina (Ginger Rogers), helps him by being very supportive. Barnaby is worried that the formula is only 23% effective, while Edwina encourages him by saying that as per his own observations, one old chimpanzee Rudolph was looking rather glossy, after drinking the formula.Edwina and Barnaby have next to no social life as he is totally immersed in his work. Hank Entwhistle (Hugh Marlowe) is a friend of Edwina and Barnaby and an ex-flame of Edwina. Edwina is content in her limited life with Barnaby, while hank is a lawyer and marrying her would have been a life of excitement and away from the daily household chores.
Barnaby is urged on by his commercially minded boss, Oliver Oxley (Charles Coburn), who has already gone ahead and made ad copies for the miracle elixir drug that Barnaby has been working on. But then, Barnaby figures out that the chimpanzee showing signs of rejuvenation is not the old Rudolph at all. It's a 6-month-old chimp and hence only acting its age.One of Dr. Fulton's chimpanzees, Esther, gets loose in the laboratory, mixes a beaker of chemicals, and pours the mix into the water cooler. The chemicals have the rejuvenating effect Fulton is seeking.
Unaware of Esther's antics, Fulton tests his latest experimental concoction on himself and washes it down with water from the cooler. He soon begins to act like a 20-year-old (his eyesight gets better, and he can remove his thick specs) and spends the day out on the town with his boss's secretary, Lois Laurel (Marilyn Monroe). Fulton goes to get a new haircut, and a new sports car, and Oxley sends Lois to look for him at all the Ford agencies in town. Lois finds Fulton, but he takes her in his new car, and they go around town. Fulton drives recklessly and crashes the car. As he put it into a garage, they go roller skating, diving at the pool, even getting a innocent kiss on the cheeks from Lois. By evening, the effect of the elixir fades and Fulton reverts to his usual old state.
Edwina is worried when Fulton doesn't return home and visits him at his lab. When Edwina (Ginger Rogers), learns that the elixir "works" (she is particularly concerned about the lipstick all over Fulton's face and the fact that he intends to do more experiments on himself), she drinks some along with water from the cooler and turns into a prank-pulling schoolgirl. She puts a live fish inside Oxley's pants. She changes into a frock and drives Fulton's new car. They go to their honeymoon hotel and check into the bridal suite. They end up dancing all night and then Edwina starts crying when she thinks Fulton is insulting her mother. Edwina throws Fulton out of the room without his glasses. Fulton falls down the laundry chute and bangs his head and passes out.Fulton finds Edwina the next morning and they both go home.
Edwina makes an impetuous phone call to her old flame, the family lawyer, Hank Entwhistle (Hugh Marlowe). Her mother, who knows nothing of the elixir, believes that Edwina is truly unhappy in her marriage and wants a divorce (she was anyways more amiable towards Hank from the very beginning)when Edwina and Fulton reach home, Hank and Edwina's mother are already there with the divorce papers and the press. Edwina throws Hank out and tells Fulton that it was all her fault. Fulton blames Edwina for having hidden feelings for Hank, but Edwina explains that Fulton kissed Lois, but he doesn't have any feelings for her. It was the elixir.
Barnaby takes more elixir (Edwina makes him coffee out of water from the cooler). They are both called by Oxley for a board meeting where Oxley wants Fulton to sell him the formula for any sum he demands. Oxley drank the formula the previous night but had no effect (no water from the cooler), and thinks that Fulton is hiding a secret ingredient. But Fulton and Edwina are deep in the effects of the formula and Edwina plays pranks on Lois, for kissing Fulton. They both run away from the board room. Edwina and Fulton fight like kids on the way home and throw paint at each other. Edwina again calls Hank, who promises to come over.Fulton befriends a group of kids playing as make-believe "Indians" (Native Americans). They capture and "scalp" Hank (giving him a Mohawk hairstyle), later fleeing when police show up. Meanwhile, Edwina lies down to sleep off the formula. Meanwhile, a woman leaves her baby with the Fulton's' housekeeper as she needs an emergency babysitter. When Edwina awakens, a naked baby is next to her and Barnaby's clothes (he changed into Injun clothes to play with the kids) are nearby. She mistakenly presumes he has taken too much formula and regressed to a baby. She takes the child to Oxley to resolve the problem. Together the two attempt to find an antidote and when the baby grows sleepy, Edwina tries to put him to sleep in the hopes of reversing the effects.
Meanwhile, more and more scientists (and Mr. Oxley) at the laboratory are drinking the water and reverting to a second childhood. The formula is lost with the last of the water poured away. As the water is poured away, Barnaby crawls into the laboratory through the window and lies down to sleep next to the baby. Edwina later discovers him and realizes her mistake with the baby.Later at home as Barnaby and Edwina are planning to go out, their spirits and marriage renewed, Barnaby notes that "you're old only when you forget you're young."
