Bill and Ted are high school buddies starting a band. They are also about to fail their history class—which means Ted would be sent to military school—but receive help from Rufus, a traveller from a future where their band is the foundation for a perfect society. With the use of Rufus' time machine, Bill and Ted travel to various points in history, returning with important figures to help them complete their final history presentation.

A fleet of Martian spacecraft surrounds the world's major cities and all of humanity waits to see if the extraterrestrial visitors have, as they claim, "come in peace." U.S. President James Dale receives assurance from science professor Donald Kessler that the Martians' mission is a friendly one. But when a peaceful exchange ends in the total annihilation of the U.S. Congress, military men call for a full-scale nuclear retaliation.

Life's questions are 'answered' in a series of outrageous vignettes, beginning with a staid London insurance company which transforms before our eyes into a pirate ship. Then there's the National Health doctors who try to claim a healthy liver from a still-living donor. The world's most voracious glutton brings the art of vomiting to new heights before his spectacular demise.