A typical day in Orbit City starts when George's alarm clock ejects him from bed so he can shower, get ready for work and begin his day. After a breakfast mishap with the Food-a-Rac-a-Cycle, the Jetsons move on as George leaves for work as Mr. Spacely demands his presence ASAP, Judy is pouting over her breakup with her rock star boyfriend Rex Saturn, Rosey takes Astro for his morning walk, and Elroy goes downstairs to work with Henry Orbit on his latest project, the time machine. At Spacely Space Sprockets, George arrives late and is taken into his boss's office. But Mr. Spacely is angry for another reason; W.C. Cogswell, his chief business rival, is beating him out on various projects he's originally devised. Spacely suspects there's a spy in his plant and makes George investigate. He sneaks into Cogswell Cogs disguised as his robot watchdog Sentro and learns the truth that his own work computer RUDI is the leak as he's being seduced by a sexy female computer named SARAH. George returns to Spacely's plant telling RUDI he knows he's the leak and must report him to Mr. Spacely. But he's able to delay George long enough before Spacely leaves for the day. This gives George until the next day before he has to come forward with what he's learned.
Meanwhile, a million years in the past in Bedrock, Fred wakes up to start his day (forcefully) as his bird alarm clock calls in Dino to greet him and get him out of bed. After a cold shower, Fred can smell his favorite breakfast and figures Wilma is up to something. He telephones Barney next door, notifying him of her plot of her trying to sweet talk him into planning an expensive vacation to Honolurock. Betty's already at his house as she and Wilma try to give him a hint by dressing up in hula dancer outfits. He intentionally ignores their signals and leaves with Barney for work at Mr. Slate's quarry. But while on their break, Fred reveals a plan where he indeed wants to treat the wives to their desired trip. He wants to pool his and Barney's money for a high stakes poker game at the Water Buffalo Lodge later in the evening. Fred says he feels lucky just before Mr. Slate enters the conversation and announces it's his and Barney's lucky night as they're due to work the late shift in hope Slate's company can outproduce that of his rival Turk Tarpit. But at the end of the work day, Fred decides to leave the dinosaurs to work on their own as he and Barney leave for the lodge anyway. As they arrive, they see Mr. Slate just outside as he's entered as a player in the poker game. Undeterred, Fred takes Barney to a costume store where they disguise themselves as a Texarock tycoon and his girlfriend and get themselves into the game. With Barney giving signals and making distractions, Fred cleans up at the game as all the players except Mr. Slate have been eliminated. The two play one last hand for all the money in the pot. But a spider prevents Barney from warning Fred to fold upon seeing the boss having a better hand. Not only does Fred lose the game, but Barney loses his wig and both are discovered and subsequently fired by Mr. Slate.
Back in Orbit City in the future, George ponders how he's going to turn in RUDI to Mr. Spacely until he hears a noise in Elroy's room, and sees Henry Orbit leaving in shock. He sees an unusual contraption and when his son explains it's the time machine he's been working on, he doesn't believe him, and then is shocked as well when Elroy lets a harem girl from ancient Persia out of his closet as proof. She gets a little too close to George when Jane is about to check and Elroy tells him to place her by the machine while he stands by the door as the boy returns her to her time without either parent seeing it. But because George did see something, he decides to give the time machine a try to help him forget about his situation at work (for a while at least). Jane decides to go along, as does Judy to get away from her boyfriend problems. Elroy sets the machine for the 25th century, but when Astro comes as well, he hits the time lever with his tail, dropping it to the past setting. Elroy activates it and the family vanishes with the machine just before Rosey enters to call them for dinner, leaving her wondering where they've all gone.
Back in prehistoric Bedrock, Fred and Barney are driving their wives, who are blindfolded, to their vacation destination. They haven't broken the news they were fired from their jobs, so the best they do is take them camping in the forest outside Bedrock. Wilma and Betty are quick to complain that their husbands are cheap as conditions are far from ideal. Dino's eaten all their food, biting bugs are flying all over, and giant ants try to make off with the tents. The guys are just able to retrieve them and decide to set up camp when flashing lights appear all around them, putting them in a panic. They try to get the wives to leave with them, but instead, Wilma and Betty decide to stay and investigate to their husbands' reluctance. The Jetsons arrive nearby and look around thinking they're in the 25th century. George thinks people of the future are significantly larger as a result of super vitamins and steroids. Fred thinks there might be a primitive tribe of people nearby. Each side approaches one another cut off by a large bush. Fred decides to peer over boosted by Dino while George does the same via his anti-gravity belt. They get a close look at each other and are initially frightened. Both sides back off pondering whether or not the other is friendly. They send out their respective pets and after a slow approach, Dino and Astro scare each other and make their respective groups scatter. They hide behind a tree and a boulder respectively, then look outward toward the other. They begin communicating and both groups decide the other is indeed friendly and come out of hiding to meet one another.
After the Space and Stone Age groups meet, the Flintstones and Rubbles are impressed by the Jetsons' time machine. Barney tries out George's anti-gravity belt, but bungles it to the point where he gets stuck on a petrified tree. Elroy opens an expand-o-matic bag and gives his father a pair of magnetic gravity boots so he can climb up the tree to get Barney down. Fred is further captivated by the various gadgets, especially when George uses one to control Astro when he starts chasing Dino around. Elroy's not able to get the time machine working for the family to return home, but says he will eventually. The Flintstones offer to have the Jetsons stay with them for a while as their guests as Fred comes up with a new scheme to have the future family and their devices help him and Barney get their jobs back at the quarry. After the Jetsons get acquainted with the Stone Age accommodations, Fred and Barney take them to the annual Slate Rock & Gravel picnic on the weekend to set their plan in motion. While the wives go on the rides, Judy attends a concert by rock star Iggy Sandstone. They instantly hit it off as he dedicates his newest song to her and they dance together. Meanwhile, Fred introduces George to Mr. Slate, who's initially reluctant to have them around as he and Barney are ex-employees, but welcomes the opportunity when he sees George fly with his anti-gravity belt and Fred insures he can help him finally win the picnic games against his rival Turk Tarpit. Slate wins the dinosaur shoe pitching contest with the help of the magnetic gravity boots, enabling Fred and Barney to get their jobs back at triple their salary. To earn vice-presidency, Fred enters the next contest, a race on hot coals, which he wins with the help of the anti-gravity belt. Mr. Slate is hesitant of making Fred a partner though, but when he has difficulty in the final contest, catching a pigasaurus in mud, he decides to get help. George activates the animal controller. But just when Slate almost has the contest won, Dino and Astro disrupt the action with another chase which scares the pigasaurus away and he winds up in Tarpit's hands, and once again, he's declared the winner. Slate is outraged and fires Fred and Barney all over again.
Back in futuristic Orbit City, Rosey begins to worry about the Jetsons and gets Henry Orbit to set up the time machine recall unit in hopes the family can be retrieved. They, along with the Flintstones and Rubbles return to the forest outside Bedrock as Elroy tries to get the time machine working. He still has trouble until Barney bangs it with his club and surprisingly it activates and is ready to go. George feels sorry he wasn't able to get Fred and Barney their jobs back, but they're fortunate the wives didn't find out--that is until they overhear their conversation and promise to give them a major beating. But they choose to remain civil until the Jetsons get a picture of the Stone Age gang before leaving. George has their camera set to take the picture, but at about the same point in the future, Henry starts the recall unit, which activates the time machine in the past, taking it, along with the Flintstones and Rubbles, who are standing under it, into the future, leaving the Jetsons stranded a million years in the past.
Rosey, Henry, and Mac await the Jetsons' arrival, but when the time machine appears, they think they've changed significantly before realizing it's not them. The Flintstones and Rubbles explain they've gone to the future by mistake and Henry tries to fix the machine to try again. Rosey tries to make the Stone Age group as comfortable as best she can as they try out all the various household machines of the future. They're complicated enough before Spacely barges in looking for George. He's initially skeptical when Fred and Barney explain who they are, but when Henry gets blasted in a failed attempt to fix the time machine, Spacely finally believes them, which gives him the idea to have the cavemen become promotional sponsors for his company, as he's now unconcerned for George being stranded in the past.
Back in prehistoric Bedrock, George tries to give a confidence-boosting speech regarding his family's predicament to them, but it's unnecessary as they seem to be taking it in stride. They make due with the various Stone Age animals and gadgets, but when resources run low, it's up to George to get a job so the family can generate some income. His first try is with Mr. Slate, who's already angry with Turk Tarpit in his office. Slate is about to throw them both out before Tarpit mentions George's flying and other special tricks he displayed at the recent picnic. As he makes an offer to George to work for him, Slate intercedes, willing to have Jetson as his employee. The two businessmen agree on a joint promotion as George can work for them as "The Man from Out of This World". He starts off with shows in Bedrock advertising their respective companies, then puts on more "Man from the Future" shows in various cities, including Rock Vegas, which become a booming success. George earns tons of money and is able to purchase some condos and a number of properties in downtown Bedrock. He spreads his newfound wealth to the family, enabling Jane to buy a few department stores, beauty salons, and health spas, while Judy buys a record company and becomes the new manager for Iggy Sandstone's band.
In future Orbit City, the Flintstones and Rubbles are becoming a huge media sensation as the "Cavemen from a Million Years Ago". Fred can't help himself as the newfound fame goes to his head and begins to hog the spotlight, going on various news and talk shows. He and Barney are later given a tour of Spacely Space Sprockets by Spacely himself as he reveals his plan to make Fred his Stone Age Sprockets spokesman, still unaware that RUDI is his industrial leak. Sure enough, he spills the beans to Cogswell's spy computer SARAH. At the executives conference the following morning, Spacely indeed shows Fred off to the CEOs, but Cogswell is able to transmit a hologram into the meeting and announces Barney Rubble will be the Stone Age spokesman for his company. The executives are immediately charmed into signing with Cogswell instead of Spacely, leaving him pleading to come back to him as they all leave the conference. Fred is also outraged and vows to get back at Barney, who's now becoming more popular. With the spotlight stolen from him, Fred becomes drastic and tries to throw Barney out the window at the Skypad Apartments. Wilma and Betty stop him, but begin to argue themselves as they let him go. Barney loses his grip and falls, but fortunately not too far and returns to the Jetsons' apartment just a little dizzy.
Meanwhile, in prehistoric Bedrock, problems arise for the Jetsons as their various business ventures begin to overwhelm them. George is responsible for getting downtown Bedrock back to normal after plumbing troubles at one his condo units cause a huge flood, and even helping out the fire department which he now owns, with getting down sabertooth tigers out of trees. Even Mr. Slate abandoned his company moments after making George partner, leaving him to deal with the Digging Dinosaurs Union when they go on strike. Jane also has a number of problems with the department stores, salons, and spas, and didn't even realize she owns a lake. And Judy is again having rock star boyfriend problems when she sees Iggy getting mobbed by groupies. When their financial advisor Mr. Goldbrick comes by announcing he made some bad investments with the bank, they decide to give up ownership of their properties and get out of their hectic life in Bedrock.
Back in Orbit City, Henry is still having trouble repairing the time machine. Rosey realizes a more sophisticated computer is needed to help them, so she goes to RUDI at Spacely Sprockets to get some much-needed cosmo quotinets to get it working properly. SARAH interrupts them and orders RUDI to get rid of Rosey, but he declines as he indeed cares for George and agrees to help her get the family back. Later, RUDI via the visaphone provides Henry and Rosey the data needed to get the time machine working again. And with the flick of the on switch, it's activated and ready to go. It needs to be manually operated, so Rosey volunteers since it's her family who took the risk, and she needs to take the chance as well. Mac and Henry wish her good luck as she vanishes with the machine. She first winds up in a medieval forest and narrowly avoids getting caught in a joust between two knights. She just makes it back to the machine to try again when one of them starts cutting down the tree she landed on. Back outside of Bedrock, the Jetsons with Dino are taking a drive into the forest and realize they're near the spot they landed in the time machine. They stop to relax and contemplate, hoping the time machine would be here. They long for home, but with no machine, there's no chance of their ever returning. They get stuck on a rock when they're about to drive off. Elroy thinks it could be an omen. George doubts it, but to their surprise, Rosey and the time machine land on their very spot and the family is overjoyed to see her, as she is them. Elroy resets the machine for the return trip home and they're about to leave when Iggy catches up to Judy to reconcile with her. She still has feelings for him as well and now is at a crossroads. George gives her the chance to decide if she wants to stay with Iggy or return home. She's heartbroken, but decides to leave with her family as she kisses him goodbye as he can only watch perplexed as to where she's going.
Mr. Spacely returns to the Jetsons' apartment feeling he's a ruined man as a result of Cogswell's subterfuge. He doesn't care if the Jetsons and Rosey are gone, but moments afterward they all return with the time machine and George is actually happy to see his boss again, giving him a hug. He continues griping about Cogswell until he sees the family has brought something else with them; the Flintstones' car! Again, Spacely gets another money-making idea, but George warns him not to give away too much as a result of RUDI (who greets him home via the visaphone) being the leak. However, Rosey assures him he's gone straight as it was his computations that enabled her to get the family back to their own time. Spacely puts his plan in motion as his company is producing thousands of replicas of the Caveman car. Cogswell can only wonder what's going on as SARAH is no longer able to get any more info from RUDI. He decides to send another spy in her place. At the factory, Fred sees his car will be the latest sensation when Barney arrives to see for himself. Fred accuses him of being a spy, but Barney swears he's quit Cogwell Cogs in favor of their friendship. An alarm goes off and Astro points out the real spy--Sentro, Cogswell's robot spy dog who's filmed Spacely's latest plan. The guys split up in an effort to catch him. Fred and Barney give chase on a rafter until Sentro spills tacks in their path, causing Fred to nearly fall. Barney saves him just in time and Sentro gets by George and Astro and nearly escapes until he bumps into Dino, who's arrived at the plant with Wilma and Betty. With Astro, they're able to stop the robot and ruin the film, thwarting Cogswell for sure. George agrees the two animals actually make a good team, as do Fred and Barney with each other as Fred is grateful Barney was able to save him. Their friendship is recemented when Fred hugs him.
Some time later, back at Spacely Sprockets, the Caveman car becomes the latest sensation for nostalgia buffs and the replicas are being snapped up by customers like hotcakes. Cogswell is there interested as well and decides to buy one, too. Spacely assures he has every patent, so if Coswell copies even one part of the car, he'll sue and take his entire company. Spacely enjoys tormenting his rival for once and rewards George by not docking any salary for the time he was away from the company. Any promotion is denied for the moment. Everyone's happy except Judy, who still misses Iggy. But when a young man resembling him asks her to join him for a snack, she can't resist and is back on her feet in the game of love. Fred and Barney are glad everything's going well for George, but they long for home to Bedrock, save for Mr. Slate. But luckily, Jetson took his partnership contract with him and hands it over to the guys, which will enable them to get their jobs back at the quarry. But unfortunately, Elroy gives the bad news that the time machine underwent a complete breakdown after his family's return trip home, leaving Fred and Barney saddened by the prospect of being permanently stranded in the future.
Mr. Spacely is elated that nearly all the cars are sold. He wants to use the time machine to get even more Stone Age items and animals, but the families break the news the time machine's no longer working. With the Stone Age group stranded, the Jetsons offer them accommodations until they can find a place of their own. Spacely allows the Flintstones to take their car back for old time sake, that is, once the group denies him the chance to charge them a price for it. They, Dino and the Rubbles sit down in it for that small touch of home and are about to drive off when it begins to glow, which has everyone puzzled. Elroy suspects they and the car absorbed some of the time machine energy, but George simply thinks the car wants to go home as much as they do. The Stone Age group begins to vanish and all say goodbye happy everything is returning to normal with Fred giving off a resounding "Yabba Dabba Doo", overjoyed he and his gang are returning to Bedrock.