Act One
Outside of Grauman's Chinese Theater in 1927 ("Overture"), celebrity news reporter, Dora Bailey, interviews Monumental Pictures' president R.F. Simpson, director Roscoe Dexter, actress Lina Lamont, her co-star and supposed fiancée Don Lockwood, and Don's best friend and composer, Cosmo Brown. After being pressed by Dora and the audience in attendance, Don recaps his early days as an aspiring actor and vaudevillian, how he met Cosmo, and got his start in show business, which ultimately led to a talent scout seeing both Don and Cosmo's talents and recruiting them both for bigger projects. ("Fit as a Fiddle")
Inside the theater, fans applaud a screening of the latest Lockwood-Lamont picture, The Royal Rascal, as Don hastily pulls Lina off-stage during their post-film speech. Lina, who is revealed to have a harsh, nasally voice, proclaims Don to really be her "fee-yan-see" in spite of Don's clear resentment of her as well as the entire engagement being nothing more than a publicity stunt. Processing his feelings on the matter, Don decides to walk to the after-party being held at R.F.'s mansion, where he is accosted by crazed fans. Don manages to dissuade them by pretending to be a normal passer-by, claiming to be the boyfriend of a nearby woman. When the woman tries to call the police on Don, she eventually recognizes him and introduces herself as Kathy Selden, a stage actress. Unimpressed with Don's "pantomime on the screen", the two of them trade insults back and forth, with Don becoming completely smitten over Kathy ("You Stepped Out of a Dream"). When a crowd begins to form around Don, he quickly escapes the commotion as a mob of women tear off his jacket sleeve. During a transition, the men, now left behind by their dates, dance with a new group of women as the scene moves to R.F.'s mansion, where an already intoxicated Lina sings along. ("Temptation Tango")
At R.F.'s party, a demonstration of a "talking picture" is shown to the party-goers, with everyone visibly disturbed and conflicted at the revelation of the gadget. Afterwards, Lina tries to flirt with Don, only to be interrupted by Kathy jumping out of a massive cake, revealed to be nothing more than a showgirl who performs a dance routine for the guests ("All I Do"). Enraged that Don has found out her true occupation and annoyed by his constant belittlement, Kathy throws a pie at Don, only to end up hitting Lina. Kathy runs off in embarrassment, leaving Don regretful ("You Stepped out of a Dream (Reprise)").
Three weeks later, Don is on the set of his newest film, The Deuling Cavalier, still heartbroken over losing Kathy. Cosmo tries to cheer Don up by reminding him of his acting chops ("Make 'Em Laugh"), before Dexter and his assistant directors begin filming. Lina reveals to Don that she had Kathy fired from her job at the Coconut Grove, causing Don to explode at her. R.F. interrupts the shoot to halt production, as Warner Brothers' latest film, The Jazz Singer (a talking picture), was a smash hit in spite of everyone's predictions of failure. Realizing "talkies" are the way of the future, R.F. orders Cavalier to be converted into a talking picture, much to the annoyance of Dexter and his crew.
While filming a musical on another lot ("Beautiful Girl"), director Sid Phillips has Kathy, who was one of the dancers in the number, perform for R.F. for a chance at an upcoming role ("Lucky Star"). Cosmo, who performs the music for Kathy's audition, tells Don of his discovery, allowing Don to reunite with Kathy. Learning of Kathy's connection to Lina, R.F. hires Kathy in secret, as Don takes Kathy out to lunch and professes his love for her ("You Were Meant for Me").
Don and Lina take diction courses in order to perfect their speech for their upcoming movie ("Moses Supposes"), as Dexter and his crew struggle to record Lina's lines efficiently ("Moses Supposes (Reprise)"). At the preview for Deuling Cavalier, the entire showing goes awry due to Lina's flat delivery, Don's uninspired improv, and the sound going out of synch from the picture. Scheduled to open in less than six weeks, the film looks to be the end of Don's screen career. After jokingly suggesting a return to vaudeville, Kathy recommends turning Cavalier into a musical to save its reputation. Don and Cosmo enthusiastically agree, and celebrate the brilliant idea ("Good Mornin'"). However, when Don realizes Lina won't be able to act or sing, Cosmo comes up with the idea to dub Lina's lines over with Kathy's vocals. Don is hesitant, believing Kathy would waste her career away, but agrees only after Kathy persuades him to do it. That night, after dropping Kathy off at home, Don dances in the streets on a cold, rainy night. ("Singin' in the Rain")
Act Two
As reshoots begin on the newly-renamed The Dancing Cavalier, Kathy begins to record over Lina's lines in secret. ("Would You?") Don and Cosmo are thrilled over the progress being made on the film, but the excitement is ruined by a scorned Lina, who, thanks to her best friend and fellow actress, Zelda Zanders, finds Don and Kathy together. After Don reveals his intent to one day marry Kathy as well as Monumental's plans to not only re-record Lina's songs and dialogue but to also give Kathy a full screen credit, Lina runs off to her dressing room, distraught. Cosmo and Don calm Kathy's nerves as Lina laments to Zelda about Don's lack of romantic interest in her. ("What's Wrong With Me?")
R.F. remains steadfast in his commitment to promoting Kathy's big debut, in spite of Lina's threats. As Dexter ponders how to film Cavalier's final dance number, R.F. suggests "tap dancing! We've got to have tap dancing!". With that, Cosmo helps R.F. and Dexter visualize a big production number featuring an elaborate tap sequence under the pretense of a modern framing device ("Broadway Ballet"/"Broadway Melody"). R.F., still unconvinced, asks Cosmo to do the whole number over again. Cosmo exaggeratedly passes out in exhaustion.
At the premiere of The Dancing Cavalier, Dexter and R.F. learn from Rod, the head of Monumental's publicity department, that newspapers all over town are publishing articles claiming Lina to be singing her own songs. As Rod bemoans the lack of communication and the money wasted on Kathy's campaign that will no longer come to fruition, Lina approaches the trio, revealing that she had read a clause in her contract that allows her to control her own publicity, not the studio. A defeated R.F. has no choice but to agree to Lina's demands at the risk of a lawsuit, in addition to forcing Kathy into becoming Lina's permanent vocal replacement without credit.
After the showing, Don, Cosmo, and Kathy celebrate their hard work as Lina reveals her scheme to ride off Kathy's success. As R.F. struggles to stand up to Lina and Rod continues complying to Lina's demands, Don plots to reveal Lina's deception to the audience in attendance by having her deliver the post-screening speech instead of him. When the audience becomes confused at Lina's real voice over the one she used in the movie, they demand she sing. R.F., Don, and Cosmo force Kathy to sing backstage into a microphone for Lina to lip-synch to, reminding Kathy of her iron-clad contract with Monumental. Feeling betrayed, Kathy breaks up with Don as she begins to sing for Lina. ("Would You? (Reprise)") However, Don raises the curtain on Lina to reveal Kathy singing in her stead, as Cosmo takes over to sing for Lina instead, humiliating Lina into running off-stage. Kathy tries to flee through the crowd, but is stopped by Don, who tells the audience that she, is in fact, the real star of the picture ("Lucky Star (Reprise)"). The two embrace as the show ends. ("Singin' in the Rain (Reprise)" and "Bows")
