It starts when Smithers and Mr. Burns are in Mr. Burns office and Mr. Burns get chest pains. Smithers calls the doctor and the doctor says Mr Burns suffers from a severe case of indigestion.
Lisa sits in a school bus next to Martin and they are talking about Lisa´s mouse that she has in a cage in her lap. Bart takes the mouse out of the cage and drops him out of the window and the mouse runs into the nuclear powerplant. Bart and Milhouse run after the mouse into the powerplant. In the powerplant Homer is on the way to help Mr. Burns. They put Homer in a machine to make him very small. When they are putting the laser on the machine to make Homer small, Bart and Milhouse run close to the machine so they also become small. The small Homer goes into Mr. Burns mouth and down to the stomach to help him. During the time Homer is down in Mr. Burns stomach, Bart and Milhouse see a candybar. Smithers puts the candybar into Mr. Burns mouth without knowing that Bart and Milhouse are on it. Down in the stomach, Homer sees Bart and Milhouse and picks them up. When Homer is on his way to pick them up he destroys the thing in Mr. Burns stomach so he doesn't have to have pains anymore. They all go up again trough Mr. Burns mouth and become big again.
When Bart comes up from Mr. Burns stomach, he sees Lisa's mouse and he catches the mouse and goes home.
In the end of the comic, Bart and Homer sit in front of the TV. Marge asks them how their day has been and Homer answers - "The usual".