Plot
In 2688, humanity exists as a utopian society due to the inspiration of the music and philosophy of the Two Great Ones: William "Bill" S. Preston, Esq., and Ted "Theodore" Logan. One of the citizens, Rufus, is tasked by the leaders to travel back to San Dimas, California in 1988 using a phone booth-shaped time machine to ensure that the young Bill and Ted, two dim-witted high school students, successfully pass history class. The boys are on the brink of failing the course and out of school, and their only hope of passing is if they get a perfect score on their final history report, in which they must give an oral presentation on how historical figures would view the present San Dimas. If they fail, Ted's disagreeable father, police Captain Logan, plans to ship Ted to a military school in Alaska, ending Bill and Ted's fledgling band, Wyld Stallyns, and altering history.
Rufus finds the duo at a Circle K, struggling to finish their report and offers help before another phone-booth time machine arrives and future versions of Bill and Ted step out. After assuring the present-day Bill and Ted that Rufus's claims are valid and that they can trust him, they disappear in the time booth.
Rufus shows Bill and Ted how to operate the time booth, taking them back to 1805, where they find Napoleon Bonaparte leading his forces against Austria. As Rufus, Bill, and Ted return to the present, Napoleon gets thrown by a cannonball explosion into their wake and gets dragged through the Circuits of Time along with them. Rufus explains that time will progress normally for Bill and Ted and that they cannot miss their class presentation the next day. He then departs, leaving the empty time booth for them. As they discuss where to go next, they discover Napoleon stuck in a nearby tree, inspiring them to abduct historical figures and take them to the present for their school presentation. They leave Napoleon with Ted's younger brother Deacon and ask him to take Napoleon out to town before they go.
They befriend Billy the Kid in the Wild West and Socrates in ancient Greece before stopping in 15th-century England, where they fall in love with princesses Joanna and Elizabeth. Their father tries to have them executed, but Billy and Socrates help them escape. The booth, its antenna damaged by an attacking knight in the process, takes them to 2688, where they discover that society reveres them and their future band. They are inspired to complete their report with "extra credit" by abducting Sigmund Freud, Ludwig van Beethoven, Joan of Arc, Genghis Khan, and Abraham Lincoln. After a brief stop in prehistoric times to repair the antenna, they program the booth to return to the present, but end up outside Circle K the night before, where Rufus first introduced himself. They convince their earlier selves of Rufus's trustworthiness before he explains how to get to the next day; he further warns them that they have only two hours left before their history report is due.
When they arrive at the current time, they leave the historical figures at the local mall to learn about San Dimas while looking for Napoleon. After learning that Deacon has abandoned Napoleon at a bowling alley, Bill and Ted track him to a local water park. Back at the mall, the historical figures become fascinated but also overwhelmed by San Dimas culture, and are soon arrested for inadvertently causing mayhem. Captain Logan, determined to break up Bill and Ted's friendship, refuses to release their historical figures and orders Ted to start packing up for military school.
The boys execute an escape plan based on using the time booth in the future to set up what they need in the present. They break their friends out of jail, then present each to the assembled school using stage lighting effects and rousing music. Their "report" earns a standing ovation, they pass the course, and they return the historical figures to their own times.
Sometime later, Rufus returns, accompanied by the two princesses he has rescued from arranged marriages. He says that they will also be part of Wyld Stallyns and that the four of them will change the world with their music. He asks to jam with them, but on hearing their fledgling attempts to play, he turns to the movie audience and assures them "They do get better."