"Once Upon a Time" is the thirteenth episode of the third season of The Twilight Zone, and was first broadcast in December of 1961. It starred Buster Keaton as disgruntled janitor Woodrow Mulligan, and featured Stanley Adams as his comic relief, Rollo.

Mulligan is a janitor living in the late 19th century, who is incensed by modern times, with its fast-moving bicycles, unruly youths playing trumpets, and expensive food. Luckily, Mulligan is also the janitor for an inventor who has devised a time helmet, a device that allows the wearer to travel through time. Mulligan visits the 1960s, where he meets Rollo, and after some unusual incidents, learns that he would rather be back in his own time.

There is nothing very original about this story, since The Twilight Zone has dealt with temporal dislocation in stories such as "Walking Distance", "The Trouble with Templeton", and "The Execution". What is different about this story is that it stars one of the great slapstick actors of the silent age, Buster Keaton. Also, the scenes set in the 19th century are silent movies, complete with odd frame rate, piano music, and intertitles. The comic pratfalls are about what the viewer would expect: Keaton spends most of the episode running around in his boxer shorts and falling over. It is hard to describe good slapstick, and this episode has to be seen to be believed.

It is a testament to the daring and innovation of The Twilight Zone that they could make an episode in the style of a silent movie, starring an actor whose fame had waned. It also something about the range of the program--- this episode aired only a few weeks after the darkest, most serious episode yet shown, "Deaths-Head Revisited". At the rate that Rod Serling is going, the next episode might as well be a tribute to Jean-Paul Sartre.