The musical opens to a junkyard, on a special night when once a year the cats gather together to celebrate their community, the Jellicle tribe. Almost immediately they break the fourth wall and introduce the different cats of the tribe, singing about their traits and giving the audience a general understanding of who each cat is.
After this, it's time for the Jellicle Ball to take place. Victoria, a young white cat central to the play, signals this through a dance. Then Munkustrap, the principle narrator, explains that the Jellicle patriarch Old Deuteronomy will be coming tonight to choose one cat to be reborn and go to the Heaviside Layer (cat heaven). What follows is a series of songs and dance sung by cats that wish demonstrate why they should be chosen.
Munkstrap introduces the first contendor, Jennyanydots, a lazy cat who likes to sleep. As she finishes her dance, Rum Tum Tugger, the rockstar cat, begins his dance. After his dance, one of the main characters begins her dance: Grizabella, the Glamour Cat. She is old, haggard, and her former glory days are only memories now. The other cats recoil from her and she finishes her dance. Then Bustopher Jones, an elite fat cat who visits gentleman's clubs, comes on and does his dance.
Suddenly, a crash startles the cats and they all scurry off stage. Enter Mungojerrie and Rumpleteazer, twin cats who enjoy causing trouble in the neighborhood. Finally, Old Deuteronomy arrives and all the cats put on a play for him. Another crash briefly interrupts the play, but nothing is found, and it continues. After this, the Jellicle Ball commences. During the Jellicle Ball, Grizabella tries to join in and dance with the other cats, but she is too old and decrepit, and the other cats shun her.