SpongeBob and Patrick are strolling through Bikini Bottom and see Mermaid Man and Barnacle Boy in the Invisible Boatmobile, without gas. SpongeBob and Patrick push the boat over several hills.
Barnacle Boy invites them into their warehouse full of memorabilia from their T.V. show. Barnacle Boy shows them a time machine which they have never used, and warns them not to use it.
But Patrick mistakes it for a vending machine, and all of them are transported to 1954 when Mermaid Man and Barnacle Boy are young. They see Man Ray tormenting old Bikini Bottom. Mermaid Man and Barnacle Boy are unsuccessful at foiling Man Ray due to Patrick eating the tartar sauce they were originally going to trap him in.
SpongeBob and Patrick escape old Bikini Bottom, leaving their Mermaid Man and Barnacle Boy behind. When SpongeBob and Patrick return to Bikini Bottom, it is no longer called Bikini Bottom, but Man Rayopolis. They go to the Krusty Krab which now has no name.
The superheroes from their time are now dead and buried inside of the restaurant while the past superheroes now work there. Mermaid Man is the fry cook, SpongeBob's position, and Barnacle Boy is the cashier, Squidward's position realizing that they created an alternate timeline by preventing Man Ray's defeat. They go back to stop Patrick from eating the tartar sauce, but the heroes who were sent by accident believe they are impostors. The Mermaid Men fight which creates the perfect distraction for Man Ray. The young Mermaid Man and Barnacle Boy attempt to foil Man Ray with the tartar sauce, but the two Patricks end up eating it. Another warehouse appears.
SpongeBob and Patrick from a different time period emerge from the warehouse screaming "Patrick, don't eat the tartar sauce!" Another warehouse appears above of Man Ray and out fall SpongeBob and Patrick. Yet another one appears with SpongeBob saying to Patrick "I told you we had to go back further!"
Another one pops to Man Ray's left with Mermaid Man and Barnacle Boy leaping out of it exclaiming, "Up, up and away!" They both fall headfirst into the ground. Another one appears above of the previous warehouse with the superheroes. SpongeBob and Patrick appear and throw a batch of tartar sauce over the fallen superheroes from the previous warehouse.
Another one appears next to the pair of warehouses. Man Ray flies out of it, destroys it, says, "I took care of your blasted time machine!" and leaves. All of the warehouses appearing in random locations confuses Man Ray. Man Ray sits down on a log and thinks about what is happening, but gets arrested by the superheroes. Then all of a sudden, many warehouses appear all over the planet, all of them containing multiple copies of SpongeBob and Patrick.
"Back to the Past" aired in the UK on April 2, 2010, one month and a half after after the American premiere.
The original past when Man Ray is brought to justice via tartar sauce can be referenced to "Mermaid Man and Barnacle Boy III" where Man Ray is shown to be entombed in frozen tartar sauce.
Instead of a normal 11 minute episode, this is a 14-minute episode. It's not a SpongeBob Special, either.
This is because the sister episode is 8 minutes.
This episode could possibly explain why Man Ray has turned good in "Mermaid Man and Barnacle Boy III," but is evil in most other episodes after it. As they altered the future, Man Ray was never frozen in tartar sauce to later be awakened, and turned good. Instead, he went straight to jail. Thus, he remained evil.
Running Gag: Whenever there was tartar sauce, Patrick would eat it up.
When tons of objects fall down on Mermaid Man, Man Ray's head is visible and can be seen falling down on Mermaid Man's head.
SpongeBob says "jaywalking" in this episode. The term "jaywalking" and Ernest Borgnine's birth had happened in the same year.
This episode heavily uses the butterfly effect during the time traveling scenes.
This is the only episode to feature Squilliam without Squidward.
Man-Rayopolis is a play on George Orwell's 1984. The poster featuring Man Ray's eyes watching SpongeBob and Patrick with the words, "He's watching you," is a reference to 1984's famous phrase, "Big Brother is watching you."
Young Mermaid Man and Barnacle Boy were played by Adam West and Burt Ward, who played Batman and Robin in the 1966-68 Batman TV series.
Another reference to Back to the Future is that SpongeBob and Patrick time-traveled to 1954, while Marty McFly traveled to 1955.
When SpongeBob said "Man Ray's Power Glove!," it's a reference to Mattel's Power Glove.
When SpongeBob and Patrick went back to the present and found that Man Ray was taking over due to Patrick altering history, it's similar to when in Back To The Future II, Biff's 2015 counterpart altered history by giving his 1955 counterpart the Sports Almanac and then the 1955 Biff became corrupt.
There is a reference to the movie The Philadelphia Experiment II, where, due to a similar error, the Nazis had won the war and established a fascist state in America. This is similar to how Man Ray took over Bikini Bottom.
When Mermaid Man says "Let the lighthouse of justice shine on Ray Man!," He referenced the famous Ubisoft Game Series, Rayman.
When SpongeBob and Patrick are traveling back to the present, the clocks are moving backwards instead of forwards.
Near the end, SpongeBob's body color is a lot darker than normal.