After visiting the facilities of Exploration Incorporated, a company that wants to make a Mars colony by the year 2026, Lisa Simpson becomes interested in the project and decides to sign up. The family is highly against Lisa's choice, but Homer convinces Marge Simpson to pretend they support Lisa, so this way she will lose interest in going to Mars. However, this proves to be inefficient, so the whole family signs up on the project to force Lisa to give up.
During one of the tests, everyone fails except for Marge and Lisa. The project's ideologists Paul and Barry announce that a rival project is almost in completion. So instead of 2026, the launch would be on Thursday. Most of the participants give up immediately, but Marge and Lisa decide to stay on the project much to Homer and Bart's dismay.
During the launch, Marge and Lisa reconcile and decide that they do not want to go to Mars anymore, but they make their decision too late as the countdown just started. However, when the countdown reached zero, the rocket doesn't move an inch. Paul and Barry reveal that their spaceship was only the outside of a rocket and they did that only to inspire the next generation and to provide a distraction for them to abandon the project.
At home, Lisa comments to Marge that they almost went to Mars out of sheer stubbornness, to which Marge explains that this is what a mother-daughter relationship is. A fast-forward 35 years into the future in the year 2051 is shown with Marge and Lisa living on Mars. Lisa then says that she wants to leave Mars and move to Venus. During the credits, Paul and Barry are driving away from the fake launching site, planning their future business.