"42nd Street" tells the story of the trial and tribulations of staging a Broadway Show in post depression New York. Julian Marsh is a once big time producer suffering from the effects of the great depression and is staging a show, "Pretty Lady" to put him back on top.

The writers, Bert Barry and Maggie Smith, introduce him to Abner Dillion, a rich Texan who will finance the show once his "Sugar Plum", Dorothy Brock, gets the lead. Dorothy is a typical diva, full of demands and attitude. Meanwhile, "Pretty Lady`s" leading man, Billy Lalor, meets a wannabe chorus girl, Peggy Sawyer, who has missed her audition but is luckly to be in the right place at the right time to get her break.

Dorothy`s personal life brgins to impact on the show when Pat Denning, her former lover and former Vaudeville partner, turns up. He gets mistakingly linked with Peggy to the disgust of a jealous Dorothy. Julian thinks Pat is a danger to the survival of the show should Abner Dillion find out abount him, so he arranges with Andy, the dance director, to have Denning run out of town.

During rehearsals in Philadelphia, Dorothy breaks her leg and Peggy is blamed and fired. The show is on the rocks until some of the girls think that Peggy could play the lead role. Julian has to swallow his pride and follow her to the train station. He persuades her and they work night and day to turn the kid from Allentown into a Broadway Star. Dorothy returns on opening night to wish her luck and lend a hand. The show goes on and is the success hoped for and more.