In the mid 1920s in Chicago, Illinois, Velma Kelly is a vaudevillian who murdered both her husband and her sister when she found them in bed together. She welcomes the audience to tonight's show (All That Jazz ). Meanwhile, we hear of chorus girl Roxie Hart's murder of her lover, nightclub regular Fred Casely.
Roxie convinces her husband Amos that the victim was a burglar, and Amos cheerfully takes the blame. Roxie expresses her appreciation of her husband's thick skull (Funny Honey ). However, when the police mention the deceased's name Amos belatedly puts two and two together. The truth comes out, and Roxie is arrested. She is sent to the women's block in Cook County Jail, inhabited by Velma and other murderesses (Cell Block Tango). The block is presided over by the corrupt Matron "Mama" Morton, whose system of mutual aid (When You're Good to Mama) perfectly suits her clientele. She has helped Velma become the media's top murder-of-the-week and is acting as a booking agent for Velma's big return to vaudeville.
Velma is not happy to see Roxie, who is stealing not only her limelight but also her lawyer, Billy Flynn. Roxie tries to convince Amos to pay for Billy Flynn to be her lawyer (A Tap Dance). Eagerly awaited by his all-girl clientele, Billy sings his anthem, complete with a chorus of fan dancers (All I Care About is Love). Billy takes Roxie's case and re-arranges her story for consumption by sympathetic tabloid columnist Mary Sunshine (A Little Bit of Good). Roxie's press conference turns into a ventriloquist act with Billy dictating a new version of the truth (We Both Reached for the Gun) to the press while Roxie mouths the words.
Roxie becomes the new toast of Chicago and she proclaims so boastfully while planning for her future career in vaudeville (Roxie). As Roxie's fame grows, Velma's notoriety is left in the dust and in an "act of pure desperation", she tries to talk Roxie into recreating the sister act (I Can't Do It Alone), but Roxie turns her down, only to find her own headlines replaced by the latest sordid crime of passion. Separately, Roxie and Velma realize there's no one they can count on but themselves (My Own Best Friend), and the ever-resourceful Roxie decides that being pregnant in prison would put her back on the front page.
Velma again welcomes the audience with the line "Hello, Suckers," another reference to Texas Guinan, who commonly greeted her patrons with the same phrase. She informs the audience of Roxie's continual run of luck (I Know a Girl) despite Roxie's obvious falsehoods (Me and My Baby). A little shy on the arithmetic, Amos proudly claims paternity, and still nobody notices him (Mr. Cellophane). Velma tries to show Billy all the tricks she's got planned for her trial (When Velma Takes The Stand). With her ego growing, Roxie has a heated argument with Billy, and fires him. She is brought back down to earth when she learns that a fellow inmate has been executed.
The trial date arrives, and Billy calms her, telling her if she makes a show of it, she'll be fine (Razzle Dazzle), but when he passes all Velma's ideas on to Roxie, she uses each one, down to the rhinestone shoe buckles, to the dismay of Mama and Velma (Class). As promised, Billy gets Roxie her acquittal but, just as the verdict is given, some even more sensational crime pulls the pack of press bloodhounds away, and Roxie's fleeting celebrity life is over. Billy leaves, done with the case. Amos stays with her, glad for his wife, but she then confesses that there isn't really a baby, making Amos finally leave her. Left in the dust, Roxie pulls herself up and extols the joys of life (Nowadays). She teams up with Velma in a new act, in which they dance and perform (Hot Honey Rag) until they are joined by the entire company (Finale).