When Marty lies to Jennifer about going to a concert, Verne immediately wants to get an earring but Clara and Doc object. With Marty in tow, Verne stows away to the Caribbean in the year 1697 to become a pirate and get an earring. Once there, Marty is mistaken for the infamous pirate, Mac The Black. The story escalates when the real Mac The Black confronts Marty and Verne while the Spanish Armada engages the pirates in battle. When he and Verne head back to the normal future, Marty apologizes and tells the truth to Jennifer.
Mr. Wisdom, host of a children's scientific show and Verne's biggest hero, is broadcasting an episode from Hill Valley. Verne and Marty go to meet Mr. Wisdom in person and they end up bringing him to Doc's lab. Doc angrily confronts Mr. Wisdom, explaining to Verne and Marty that Mr. Wisdom was Doc's college roommate and stole one of Doc's inventions to win a science fair. Later, Mr. Wisdom breaks into Doc's lab and steals the DeLorean. Once Doc, Marty, Jules, and Verne find the culprit before landing in the volcano krakatoa in 1883 and overflowing with lava, a crazy contest is held to see who the real scientific genius is...and Verne admires a new hero.
Biff announces that he has a legal deed from the 1800s for Jennifer Parker's ranch and plans to evict her family, who does not want to be evicted. With the intention of helping his girlfriend Jennifer, Marty heads back, with Jules and Verne, to the Old West to find the truth to the matter. Once there, Marty finds out that the Parkers were swindled out of their property by an outlaw Tannen ancestor. Marty joins the gang of Thaddeus Tannen, hoping to prevent the scheme from happening. When returning to the present year with Jules and Verne, Marty angrily confronts Biff. The signature for the deed disappears, and Biff warns Biff Jr. that it is coming out of his allowance. After saving the Parker ranch, Marty gets finally kissed by Jennifer.
Verne hates taking dance lessons and asks Doc and Clara for his help. Doc tells him that he once had "blueprints" for a dance machine that helps one to remember the steps but the blueprints were lost in a fire when Doc was a young man. Verne and Marty head back to 1944, where Verne has the opportunity to meet his dance instructor, Dorothy, when she was a young girl. Escaping from Sergeant Tannen and the blackout warden, Marty accidentally joins the Army, while Verne goes to the movie theaters. When Verne dances with Dorothy while watched by Rosie, Marty begins crying in the Army. Meanwhile, Verne rescues Marty from being drafted. At the Hill Valley Jitterbug Contest, Verne wins the trophy and gives it to Dorothy, who is with her sister, Rosie. He and Marty head back to the parallel future in Hill Valley.
While playing baseball, Verne meets a new friend. Chris, who sports a baseball cap, can play like nobody's business and becomes the "hit" of the game. He and Chris begin to pal around and end up in the comic book store. Seeing an old poster of a circus long since disbanded, Verne and Chris, with Marty in the back of the DeLorean, head back into the 1930s APR 7-APR 10 1933 to see the circus in its heyday. The circus is in serious financial trouble. Farmer Tannen is about to take over the circus because the owners are unable to pay rent to Tannen for the fairgrounds. When the star high-wire act quits, Verne and Chris come to the rescue by taking over the act. Verne finds out that his buddy, Chris, is a girl. Chris (short for Christina) ends up saving Verne from a high-wire fall. Verne gives up his prejudice against "females" and saves a wonderful friendship. Marty takes Verne and Christina with him back into the 1990s.
Verne has become a video game addict. His game of choice, or addiction, is called "BraveLord and Monstrux. " After neglecting his duties because of the video arcade game, Doc and Clara ground Verne to his room and forbid him from playing video games. Jules, with the help of Marty, attempt to placate Verne by using a device that would transfer the game electronically to Verne's bedroom TV screen, thus enabling him to continue to play. Unfortunately, something goes haywire with the wiring and the characters of the game come to life, while Doc is transported into the game. BraveLord, a "He-Man" muscle man, ends up in Verne's bedroom while the vile Demon Monstrux ends up at Biff's house. Verne, Jules, Marty and Clara must defeat the Demon Monstrux, get it and BraveLord back into the game and Doc back into reality.
Jules is tired of being considered a brainiac, unpopular kid. Verne plants the idea in Jules' head to grow a money tree, which makes Jules the popular rich kid at school. Unfortunately, greed takes root. Jules spends on-credit, buying gifts for his new friends and his family (like Doc and Clara), while the money leaves ripened. Jules teaches Marty how not to let the crooks steal the tree. The news media gets wind of the money tree. The FBI hears the story and believes the tree to be a part of a counterfeiting operation. While Marty is asleep outside, Biff and Biff Jr. steal the tree in the middle of the night. When Marty and the Browns attempt to retrieve the tree, the boys almost get hurt. They all realize what money has done to their priorities and they decide to let the tree go. Biff and Biff Jr. get their rewards just when the FBI arrests them for being in possession of the tree, whose leaves turn brown after being picked. Jules ends up keeping some of his new friends because they realize that he is an okay kid.
After being teased by kids at school about his name, Verne decides that he wants a new name. After Verne finds his out that his parents named him after Jules Verne, he and Marty head back to 1800s France to convince Jules Verne to change his name. When that plan fails, they head to the Old West (where Doc and Clara first lived via the time traveling locomotive) to convince Doc and Clara to use another name for Verne, who is about to be born. Verne is depressed to find out that the other alternatives for his name are Jehosaphat and Galileo – not very appealing or cool, to say the least. Max, Marky, James Bond, Luke Perry and Bart Simpson are not considered. After Verne courageously helps out with his own birth, Clara and Doc name Verne after a very brave young man...Verne!
Doc angers Clara by causing another power outage in Hill Valley, thus affecting the upcoming Founder's Day Celebration for the next day. Meanwhile, Doc offers to fix the town's power plant by increasing its output and producing free electricity... Unfortunately, Doc's upgrades to the system causing everything electrical to turn on (and on and on.) People are unable to turn off lights, lawnmowers, hairdryers, etc... Biff decides to run Doc and his family "outta town. " The town residents rally around Biff, who decides to "fix" the power plant. Biff causes everything to explode like fireworks, including street lights, etc, and the residents turn to Doc to shut the system down. Unfortunately, there is no power for the Founder's Day Celebration, which means no rock concerts, no bash-em-up bumper cars, etc. An old man shows up and tells everyone, including Marty, Doc, Jules, and Verne with Clara, that there was no electricity when the town was first settled. The first Founder's Day was celebrated with horse shoe tossin', quiltin' bees, barn dances and chasin' greased pigs. Everyone decides to celebrate Founder's Day like the original Founders have done.
Marty parallel parks the DeLorean outside the store that Jules and Verne are in. As the comet Kahooey is about to pass the Earth's orbit, Biff declares that aliens are coming and causes the residents of Hill Valley to panic. Biff finds a "space craft" behind Doc's oleander bushes – an alien craft he recognizes from 25 years earlier and the last time comet Kahooey appeared. Biff has the military, police and assorted agencies believing that Doc is an alien. With Doc in serious trouble, Marty, Jules and Verne travel back to 1967 to straighten out the mess. Marty and the boys find that Doc has built a flying craft to view the comet and that Biff has mistaken it for an alien space ship. When Marty, Jules, and Verne appear in beekeeper suits and the DeLorean while confronting him, they make Biff promise that he will not say anything about the "visit" from the aliens – now and in the future. Biff promises and Marty, Jules and Verne head back into the future in 1992, early 1993. When they arrive, Doc is fine and Biff is trying to peddle some cheesy "alien" souvenirs without much luck.
Verne is being pressured by the bully Jackson to swing over Deadman's swamp on a rope to become a member of the Mega-Muscle-Man Club. Verne is skeptical and considered a chicken. Verne finds his father with Marty; Marty is wearing booster boots – one of Doc's new inventions. Marty explains to Doc that he will not have to stand on his tiptoes to kiss Jennifer. Verne tells them of his predicament. Jules enters with an old box of newspapers. Marty and the boys discover that Doc was involved in Small Town Wrestling in the 1950s. Doc tells them that he was set for a match but never entered the ring. Verne thinks that if his dad had become a wrestler, the other kids would really think that he was cool. Marty and the boys head back in time to make sure that Doc competes in the match. Once there, Emmett "Brain Buster" Brown enters the ring but gets conked on the head with the hanging microphone. A loopy Doc then believes that he is a superhero – Mega-Brain-Man! Wearing Marty's booster boots and the wrestling outfit, Doc scours the city, putting evil-doers in their place. As it turns out, "Mega-Brain-Man" constantly mistakes ordinary events as "dastardly" deeds and acts inappropriately. After one incident, Doc regains his memory and is taken back to the ring to finish his match, where he is defeated. He decides to continue his pursuit in science. Marty and the boys head back to the future. Verne is once again pressured to swing over the swamp and declines, saying that he will follow his instincts. Jackson grabs the rope and swings. The rope breaks and Jackson goes down into the goop, and Verne declares as he leaves, "This is Mega-Brain-Man saying yoicks and away!"
While playing putt-putt golf, Marty angers Jennifer by making fun of her hairdo (which he caused to look dreadful) and making a date with Liz (a snobbish, nasty girl in their class). Marty stops by the Browns' house to borrow money for a haircut to go out with Liz. No one is home and Marty uses a not-yet-perfected hair cutting invention to save money. The device causes Marty's hair to drastically change styles instantaneously. Einie communicates with Marty that the Browns are at the local amusement park. Marty goes to the park and finds Jules and Verne; Clara and Doc have gone off for some "lemonade" at another fair – the 1904 World's Fair Exposition in St. Louis. Using the locomotive, Marty and the boys go to find Doc and Clara; Marty needs Doc's help in fixing the hilarious affects of the hair cutting machine. Once there, P.T. Tannen (Buford's son) kidnaps Marty and displays him in a side-show as a "curiosity of nature". Doc, Clara and the boys save Marty and head home. Marty breaks his date with Liz (who has already found someone else, richest boy Milton Van Conrad the Third, to take her out) and apologizes to Jennifer for making fun of her hairdo. Jennifer and Marty then kiss.
The series finale. After Biff Jr. steals the arrowhead that Verne was going to use for his "Show and Tell", Verne takes the DeLorean to find something really special. Not thinking, he procures a dinosaur egg which hatches back in 1990s Hill Valley. Verne, with the help of Jules and Marty, must hide the fast-growing dinosaur from his family and the rest of the town. The dinosaur is in danger when Biff and Biff Jr. capture it. They, in turn, sell it to Mr. Wisdom, who plans on dissecting poor "Tiny" and making lots of money. Marty and the entire Brown family save the baby dinosaur and reunite him with his mother in prehistoric times.