Cats’ first act starts with the gathering of the Jellicle Cats. After they notice that some man is watching them from afar, the Cats tell the story of their tribes are named. When Victoria the White Cat starts the Jellicle Ball, Munkustrap announces that during that night, a new cat chosen by Old Deuteronomy will be reborn on the Heaviside Layer.
Afterwards, Jennyanydots appears and teaches the cats about mice and cockroaches. She gets interrupted by the arrival of the Rum Tum Tugger.
After Rum Tum Tugger’s arrival, a dirty old grey cat named Grizabella appears. The Cats shrink away from her because of disgust and fear. After Grizabella leaves, a fat black cat called Bustopher Jones enters. Unlike Grizabella, Bustopher looks elegant and rich. The Cats hear a loud noise and they all scamper around. After the Cats are all gone, the mischievous pair composed of Mungojerrie and Rumpleteazer take their place.
Not long afterwards, a large old cat who turns out to be Old Deuteronomy appears. He tells the Cats something about the Jellicle Cats and the Pollicle Dogs. Another crashing noise startle the Cats before they start celebrating the Jellicle Ball.
Grizabella tries to take part in the party but the other Cats do not want to mingle with her.
The second act takes place after the ball. After Old Deuteronomy sends a message that refers to Grizabella, a former Cat actor named Gus comes in. His colleague, Jellylorum, tells about his adventures and this makes Gus remember the things that he had gone through in the past.
After Gus leaves, the unofficial officer-in-charge of the night train to Glasgow, Skimbleshanks, appears. He shares the story of how a steam train engine is assembled using the things that can be obtained from the junkyard.
Another loud noise ensues and the “most wanted” Cat named Macavity comes out. His minions captures Old Deuteronomy and the other Cats try to help him. Macavity disguises as Old Deuteronomy but the Cats discover his true identity. Macavity then fights with Munkustrap and Alonzo but he is utterly defeated. Before the rest of the Cats can do more damage to him, Macavity flees the scene.
In order to bring back Old Deuteronomy, Rum Tum Tuggers suggests that they seek the help of Mr. Mistoffeless, “the original conjuring cat.” He resurrects Old Deuteronomy, letting him continue making The Jellicle Choice.
Grizabella comes in and pleads to the cats. She’s able to convince some members and she’s chosen to go to the Heaviside Layer. The play ends with Old Deuteronomy accompanying Grizabella for a while before he lets her continue the journey on her own.