The courtyard of an upscale, faux-rustic hotel resort in the area immediately outside a Northeastern college campus plays host to the fifth reunion celebration.

At midnight, upon leaving the reunion, the King reminds his best college friends, Berowne, Dumaine and Longaville, that the time has come to commit to the pledge they made at graduation. They have vowed to spend the next three years devoted to study and self-improvement, and live together, removed from all the pleasures of the world... especially women ("Prologue"). Berowne protests that vows like these go against the fun and raucous lives they should be leading as 26-year old young men ("Young Men"), but the King pushes back, and all four men recommit to their oaths. They retreat into a lodge on the hotel grounds to begin their monastic tenure.

Enter the Princess and her best college friends, Rosaline, Katherine, Maria and Boyet. Also in town for the reunion, the Princess takes the opportunity to do some business with the King on behalf of her father. The girls and Boyet have come to back her up ("Hey, Boys"). Just as the King returns outside, the Princess has second thoughts, panics and hides with her friends in the shrubbery. She explains that she had a fling with the King back in college, and the girls all bemoan their poor judgment in guys back in school ("Hey, Boys – Reprise"). The girls and Boyet return to the party for more liquid courage.

While soaking in the resort hot tub, another former classmate, Armado, seeks comfort from his "townie" pal, the bandleader at the local bar, Moth. Armado, a wealthy and flamboyant Spanish former exchange student, is in love with the barmaid at the cantina, Jaquenetta, but her indifference has made him extravagantly melancholy. Moth tries to make him feel better with a song about the unexpected objects of his own affection, but doesn't really succeed ("I Love Cats"). Suddenly, Dull, the campus security guard, enters with Jaquenetta and the bartender, Costard, in tow. Armado tries to woo Jaquenetta, but she doesn't seem interested and leaves. Alone, he sings to her with dancers and castanets ("Jaquenetta").

The Princess and her friends are back, and she's finally ready for business. The Princess rouses the men and addresses them with her complaint: the King owes her father money. But the King rebuts that; in fact, her family owes him. In the meantime, Berowne catches a moment alone to flirt with Rosaline, despite his recent vow ("Brabant Song"). The business matter between the Princess and the King remains unresolved, but the boys seize the opportunity to sneak over to Boyet to ask about the girls, and the girls recall their relationships with these very boys in college ("Brabant Song, Pt. 2"). Boyet is amused: although the boys don't seem to remember their exes, clearly they're smitten anew.

Armado writes a flowery (and slightly raunchy) love letter to Jacquenetta and gives it to Costard to deliver. Armado then bumps into Berowne, and they each recall their unlikely college friendship: Armado the romantic and Berowne the cynic ("Brabant Song, Pt. 3"). After Armado leaves, Berowne realizes that he envies Armado's openess to love and that he is indeed falling in love with Rosaline ("Change of Heart"). Berowne writes Rosaline a love letter and gives it to Costard to deliver. Not surprisingly, Costard gets the two letters mixed up.

The ladies and Boyet return, enraged that the boys refuse to negotiate with them or be hospitable enough to let them inside the lodge. The Princess says they will not budge, even if they have to stay all night in the courtyard. Enter Costard, who gives Rosaline the letter that was meant for Jaquenetta, causing all sorts of confusion. The Princess is dismissive; Rosaline is upset and takes her frustration out on Boyet. After they leave, Costard comments on their bad behavior and, joined by Dull and Jaquenetta, complains about all the rich people ("Rich People").

Two academics, Holofernes and Nathaniel, enter as the boys sing about the wonders of academia ("Academia"). The professors speak professorially until Jaquenetta appears and asks them to help her read the letter that Costard has delivered to her. The professors explain that the letter was actually meant for Rosaline. Alone again, Jaquenetta wonders whether there is any point in getting her hopes up for love ("Love's a Gun").

Berowne emerges from the lodge, sighing for his love of Rosaline. He hides when he hears the King enter, also sighing. The King, not seeing Berowne, secretly writes a sonnet to the Princess ("The King's Sonnet"). The King hides when he he hears Dumaine enter, sighing. Dumaine secretly writes a poem for Maria with Renaissance Faire backup ("Dumaine's Sonnet"). Dumaine, in turn, hides when Longaville enters, sighing. He is writing a sonnet to Katherine ("Longaville's Sonnet") which turns into an elaborate tap dance and kickline number. Dumaine reveals himself and calls Longaville out for breaking his vow, to Longaville's chagrin... but the King then reveals himself, to both men's chagrin. Finally, Berowne reveals himself, to general pandemonium. He accuses all three men of betraying him by betraying their oath. As his grandstanding climaxes, Jaquenetta enters, carrying Berowne's love letter to Rosaline. All four men are outed as having broken the vow to which they committed at the top of the show. What can they do? They turn to Berowne. With questionable logic – but excellent language skills – Berowne argues that, if they sincerely woo the ladies, they aren't really breaking their vows ("Are You a Man?"). Everyone is convinced, and the gentlemen go to prepare a series of performances to woo and wow the ladies.

The Professors encounter Armado, who explains that the King wants them to help prepare a show for the ladies. Holofernes suggests a hoary old pageant called The Nine Worthies, but abruptly changes her mind to presenting "The Tuba Song" instead. The professors, Armado, Costard, Dull and Moth, will all be a part of the performance. Everyone is thrilled by this idea. Everyone, that is, except for the Princess and her friends, who overhear Armado boasting about the plan. Why are the boys sending them love letters and putting on a show (dressing up like East German performance artists... in masks, no less)? It can't be real love, it must be boys just having a good time. In that case, the Princess argues, the best thing is to beat them at their own game. The ladies will also wear masks and switch identities so that the boys will woo the wrong girls ("It's Not a Good Idea"). Katherine, Maria and a somewhat begrudging Rosaline agree to join the charade.

Enter the gentlemen dressed as East German performance artists. They perform a complicated modern dance and woo the ladies. They then reveal themselves and are confused when the ladies do not respond with delight and kisses. As a last gasp gesture, they sing from the heart ("Labour of Love"). Unfortunately, they are each singing to the wrong girl, as they discover when the ladies remove their masks. The ladies laugh at their foolishness. All seems to be lost.

Berowne is genuinely upset at their failure and convinces Rosaline that he was being sincere in his love. She is also upset and berates the King and all the men, for making vows, just to instantly break them, as well as the Princess, for convincing her not to believe that Berowne could be sincere ("Stop Your Heart"). She runs off.

The Princess is moved by the genuine show of emotion and reveals her true feelings to the King ("I Don't Need Love"). Just as she and the King are about to reconcile, the performers enter with "The Tuba Song." Led by the example of the King and the Princess, all of the lovers are finally brought together. Rosaline reenters, making up with the Princess and reuniting with Berowne. A brass band plays, Armado finally wins Jaquenetta's affection, Nathaniel flirts with Boyet, Costard makes a pass at Holofernes... and even Moth is delighted by the appearance of Rum Tum Tugger from Cats, thus living out his feline fantasy. Dull knows that all of these rich people should be going home soon. All is well.

Then, suddenly, Mercadé enters with the news that the Princess' father has died. Distraught, she asks Boyet and the ladies to prepare to depart. The gentlemen's protests are to no avail. The ladies tell them that, if they are really sincere in their love, the boys must keep their vow and remain away from society and the pleasures of the world for one year. If they can stay true to their vow for a year, then they can all be together. If not, it was not meant to be.

There is one more performance, a song about the harshness of winter and the promise of spring ("The Owl and the Cuckoo"). As the rustics and the academics sing, the lovers make their bittersweet goodbyes before the ladies, Boyet and Mercadé depart on a wooden boat. The play comes to an end with the question of what the future will hold.