Jimmy Smith, a millionaire Bible publisher, is married to the overly frugal Sue. Jimmy thus has plenty of disposable income, and, because he likes to use his money to make people happy, he has secretly become the (platonic) benefactor of three beautiful women: Betty from Boston, Winnie from Washington, and Flora from San Francisco. Sue's best friend, Lucille, is married to Jimmy's lawyer and friend, Billy Early. Lucille is a spendthrift and delights in spending all the money Billy makes. Jimmy and Sue have a young ward, Nanette, who they hope will become a respectable young lady. At Jimmy and Sue's home in New York, many young men come to call on Nanette. Lucille advises the young people that having one steady boyfriend is better than many flirtations ("Too Many Rings Around Rosie"). Tom Trainor, Billy's nephew and assistant, works up the courage to tell Nanette that he loves her, and she returns his sentiments ("I've Confessed to the Breeze"). Tom wants to settle down and get married as soon as possible, but Nanette has an untapped wild side and wants to have some fun first.
Jimmy's lady friends are attempting to blackmail him, and he, afraid that Sue will find out about them, enlists Billy's legal help to discreetly ease the girls out of his life. Billy suggests that Jimmy take refuge in Philadelphia. Unknown to Jimmy, Billy decides to take Tom and meet the three ladies in the Smiths' Atlantic City home, Chickadee Cottage ("Call of the Sea"). Sue and Lucille, hearing that both their husbands will be away on business, also decide to take a vacation to the cottage.
Nanette wants to go to Atlantic City with her friends, but Sue forbids her to go. Jimmy, wanting to make Nanette happy, gives her $200 and agrees to secretly take her to Chickadee Cottage, with the grumpy cook, Pauline, acting as Nanette's chaperone ("I Want to be Happy"). Nanette is tired of everyone (especially Tom) trying to control her behavior and dreams of the extravagant fun she will have ("No, No, Nanette"). To tease Tom, she shows him the $200 and refuses to tell him how she got it. Tom angrily breaks off his relationship with Nanette, and, under the pretense that she is going to visit her grandmother in Trenton, New Jersey, Nanette leaves for Atlantic City (Finaletto Act I).
Nanette arrives in Atlantic City and quickly becomes the most popular girl on the beach ("Peach on the Beach"). Meanwhile, Jimmy crosses paths with his three girlfriends, who confront him with the promises he made to them ("The Three Happies"). Tom meets up with Nanette, and they resolve their quarrel, fantasizing about being happily married one day ("Tea for Two"). Lucille runs into Billy, and though she is surprised to meet him in Atlantic City, she assures him that she does not mind whether he spends time with other women as long as she's there to watch – and he comes home with her at the end of the evening ("You Can Dance with Any Girl At All").
Sue is shocked to find Nanette in Atlantic City. Nanette at first lies and said she was only visiting her grandmother in Trenton, but Sue knows that can't be true: Nanette's only living grandmother lives in Omaha. Nanette admits that she actually spent the night in Atlantic City. Against her protests, Sue arranges for her to go back to New York with Pauline. Sue overhears Billy speaking to the women and, assuming that he is having an affair with them, tells Lucille. Billy, to keep Jimmy's secret, does not deny it, and Lucille says she is leaving him. Meanwhile, Tom, shocked by Nanette's behavior, breaks off their relationship. Jimmy is oblivious to the confusion he's created (Finaletto Act II).
Billy tries to call Lucille on the telephone, but she refuses to answer. Flora, Winnie, and Betty tempt him to spend time with them instead ("Telephone Girlie"). Lucille, finding herself alone, realizes that she misses Billy, and nothing else can make her feel better ("Where-Has-My-Hubby-Gone Blues"). The truth begins to emerge as Lucille realizes that Billy can't be the benefactor of the three girls; he never has any money to spend because Lucille spends it all! Jimmy finally pays off the ladies, and finally the truth comes out: Billy hasn't been cheating on Lucille, and though Jimmy has been spending his money on the three girls, it is strictly platonic.
Nanette and Pauline, unable to catch a train to New York, return to the cottage, where Tom and Nanette make up; however, it appears that once more, Tom wants to settle down while Nanette wants to enjoy being single. Tom produces a beautiful engagement ring, and Nanette has a change of heart, now insisting that they should get married today ("Waiting for You"). Sue and Lucille decide that in order to ensure Jimmy never again has philandering opportunities, Sue must spend all of Jimmy's money herself. The show ends with a tea dance, where Sue wows Jimmy with a fancy dress and a final dance number ("Take a Little One-Step/Finale").