The Mellop family, Bill Mellop, and his children, Samantha, Michael, and Jason will be spending their first Christmas alone since their mother died. Also the plant nursery run by Bill and his sister is under threat from a difficult and mean new neighbour, Berrie Dump. Samantha sitting with her dog Ajax, notices a mysterious falling star that comes in through their window, and crashes into a crystal punchbowl. The star refracts into seven smaller rainbow coloured stars, one hitting Ajax's new Christmas collar, and another Samantha's frilly apron. Strange things begin to happen. Samantha can hear Ajax talking, but when she asks Jason to listen he hears nothing. When Jason jokingly dons Samantha's apron he too hears Ajax talking. The frilly apron must be magic.
The dog collar and the frilly apron enable the kids to communicate by telepathy. Michael's favourite T-Shirt makes him disappear and he sneaks into Dump's office. He hides the dog collar in Dump's hat to tune in to his thoughts and foil his next move. Michael tries to impress the beautiful Harmony with the T-shirt of invisibility but she tells her father Bernie Dump!
Dump orders Harmony to use her friendship with Michael to seize the apron. A strange Kombi van makes its way towards Earth with a childlike man named Alpha-Ralph 416 and an intelligent girl named Commander Gamma Jane 378. The boys try to recover the collar from Dump's home while Ralph and Jane have an unpleasant introduction to earth. Aunt Jocelyn suddenly speaks a mixture of English and German. Jane tells Samantha she knows the family has their leader and that she and Ralph are there to take him back to Moon.
Jane and Ralph have been sent by Her Royal Babiness the Grand Baby, to find the Moon's new ruler. Jane is in charge because she's younger it seems everything on the Moon is in reverse, the ruler is a Grand Baby and the kids boss the grown-ups around. There are still four items in the house with special powers of linguistic ability, flight, time travel and speed and they must be found, and placed with the apron, collar and T-Shirt so the star can be reformed and the Chosen One found. Meanwhile Harmony is showing her father the T-shirt of Invisibility.
The kids believe it was one of Aunt Jocelyn's bras which gave her the linguistic powers but try them on without success. Harmony washes the T-shirt of Invisibility in a bucket and when Dump throws the rest of the water at a barking dog it disappears. He bottles the water and sets out in his truck with a new sign, Royal Dump Pest Exterminators. Jason, wearing his baseball cap, when his feet suddenly leave the ground and he gains both altitude and speed. Bill is flabbergasted when he sees his son fall out of a tree, only to claim he didn't climb the tree but flew into it!
The Royal Dump Pest Exterminator company is making a fortune, making ants, spiders, and even rats disappear and Dump buys a new mansion. Harmony wears the baseball cap and floats away with it. The family retrieves the baseball cap from Dump, who is horrified, as the dog becomes visible again. The Grand Baby has only six or seven days to live, so the rest of the powers must be found so the new leader can be identified. The bathroom toilet bowl must give linguistic ability!
Pests sprayed with water from the T-shirt of Invisibility are re-appearing and Dump is besieged with calls from furious customers. Bill orders Michael to the nursery, leaving the others desperately trying to find the power of the toilet bowl—to no avail. Dump realises the power involves something Aunt Jocelyn uses in the bathroom and works out a plan to get to know her better.
The Grand Baby has only days to live, but attempts to reach Jane by telephone are hampered by Dump. Bill orders the kids to vacuum and Ralph is watching a dinosaur show on TV when his foot hits the power button and both he and the vacuum disappear. Ralph is nowhere around—instead he's clutching the vacuum cleaner and wandering in a primeval swamp of 300 million years ago, inhabited by giant dinosaurs.
Dump sees a pair of slippers careering around the Mellop's hall. He tries them and shoots away at great speed to the local oval where he charges onlookers for the ride of a lifetime. The kids are watching a pirate program called Swashbuckle's Fortune on TV, when Ralph reappears. Seeing the mess Ralph has made, they are all touching the vacuum cleaner when the power is switched on. They vanish and reappear on a beach—where they face a murderous band of pirates, led by the frightening Iron Peg.
The kids encounter a band of battling pirates via the Vacuum Cleaner of Time Travel but rocket back to the present—complete with Peg's leg. They estimate they now have four of the six powers unaware that Dump has the Slippers of Speed, which have since slowed down. Michael and Harmony search the Kombi for something to help Dump make another fortune but hit some buttons and find themselves hurtling into space.
The Kombi lands on the moon's surface and the Grand Baby thinks Jane and Ralph have returned with her successor. When Michael hits the Earth button, the Kombi takes off, and the Grand Baby realises Jane and Ralph can't have been inside. Jason tries to get Aunt Jocelyn back into the bathroom where they suspect the power of linguistic ability is hidden. Dump tries to steal the Kombi and Jane disables it by removing an item, which looks like a metallic golf ball but is actually a miniature nuclear reactor.
Dump learns of the cold fusion reactor and asks the kids to swap the reactor and the Kombi for the Slippers of Speed. Jane gives in to Dump's demands, but reactor has disappeared. Aunt Jocelyn has mistaken it for a golf ball and it will destroy the entire planet if struck. Ralph retrieves the reactor and returns it to the Kombi, while Dump sets up a new business venture—the full horror of which is revealed as the Kombi van dumps tonnes of garbage on the pristine surface of the moon.
The Grand Baby believes Jane and Ralph have returned with the new leader, but the Moonlings' excitement turns to confusion when the Kombi dumps a load of strange objects and departs. Michael becomes suspicious about the material Dump is dumping in space. The kids tell their father the truth about what has been going on and Bill tries to call Jane's parents on the number she has given him. Aunt Jocelyn emerges from the bathroom holding a toothbrush and speaking a foreign language. Does the toothbrush have the Power of Linguistic Ability?
Samantha wears the apron and slippers and holds the baseball cap, t-shirt, vacuum cleaner, dog collar and toothbrush, as Jane holds the punch bowl over her head, to discover if she is the Chosen One, but one of the items is still wrong. The kids decide the toothpaste had the power but Aunt Jocelyn has tossed the old tube out with the rubbish. When they find it in the garbage Samantha scrapes out a sliver—and begins to talk in a foreign language.
Samantha realises she is not the Chosen One and thinks it is Jason. Jason is draped with the items of power, but scarcely a spark is raised. Michael refuses to be tested and a crazy chase follows. Michael and Harmony investigate the nature of the garbage being left on the Moon and learn Dump is dumping disposable nappies on Moon. The kids dress Michael in the items of power while he sleeps but he is also not destined to be Moon's new leader and they decide it must be Bill Mellop. Samantha is distressed because having lost her Mum, she now has to face losing her Dad as well.
The Grand Baby is gone and the need to test Bill as her successor is vital but the Miraculous Items go missing. Michael is suspected of the theft but Dump arrives at a party draped in the items. When he realises what the outfit could mean, he plugs in the vacuum cleaner and reaches desperately for the full punch bowl. The kids are shocked to see him with the powers, but more so when they realise Dump was dumping garbage at the house the night the star struck—and chances are he could be the new Grand Baby!
Samantha realises she will not lose her dad if Dump becomes the Grand Baby so the kids decide to help, but efforts-to empty the punch bowl fail because Ralph has added the tablet which keeps it topped to the brim. As the party guests are pressured to drink litres of punch, Michael discovers Dump is peddling nuclear waste to the moon. Samantha convinces Bill to try on the miraculous items, and the Moon's Chief Minion gives her the number Grand Baby provided before she died—22,121,986. Now it's vital the kids find out what it means!
Jane, Jason and Samantha search for an equation, which will explain the Grand Baby's list of figures. Dump reassures Harmony the waste on Moon is safe but millions of miles away three Moon Drones have fallen ill after playing with one of the barrels.
The Chief Minion will free Michael but Harmony can only go free if Dump agrees to remove all waste from the moon. The mystery numbers are the birthdate of someone born in the Mellop home, but only Michael's late mother was born in the house the Minions ignore further pleas for release. Dump realising the full portent of his misdoings, and what he must do to free his daughter, brings a load back from Moon and cancels his waste contracts. But when the Kombi runs out of fuel he is unable to return for Harmony. Her only hope is to zip down a space/time corridor, which will open when the star sends the Chosen One back to Moon.
Michael grabs the vacuum cleaner, hits the power switch and disappears. When Michael reappears with an idea on who is the new Grand Baby. The kids re-assemble the magic powers and place the punch bowl over the head of their last hope. As someone disappears from the Mellops, destined to be the new Grand Baby, Harmony arrives home. Michael finds a Christmas card from his mother's and reads her last loving message—he too now believes in magic.
The Mellop kids try to use their father's new fax machine to invite the Moonlings to the nursery's relaunch party but the signal is intercepted by the Grubs, a ravenous alien species who have just invaded Peaceful Planet. Harmony and her cousin Darren have swapped homes for the holidays. Darren helps the Mellop kids log on to a pan-galactic bulletin board where they make contact with Ebony. She appears as a hologram in the Mellop's dishwasher and warns them about the destructive Grubs who are on their way to Earth.
The Grubs send a holographic fax beginning a musical countdown to their arrival in nine days. Ebony explains how the Grubs travel across the vast distances of space using Woops, Windows of Opportunity, and gives the Mellops plans to make one of their own. Samantha tries phoning the Grubs to uninvite them from the party but only excites them more to come and wreck the planet. The Grubs tell Sam they'll reconsider coming if she can send them a model of the Sydney Opera House. With dollar signs in his eyes, Dump makes the first leap through the Mellop's Woop.
After Dump steals Samantha's Woop-equipped bedroom window, the Mellop kids search for where he has hidden the window. Darren returns the window when he learns his uncle stole it. Unfortunately, the window is missing the molecular exciter that makes the Woop work. They may have trouble finding after it gets buried under a pile of manure.
Jason tries building a model of the Opera House but isn't sure what it looks like. Using instructions from Ebony, Sam and Darren build a molecular exciter detector out of fridge magnets and garden shears. The pointy end leads them to the device in Grubs' back pocket but they don't know how to retrieve it without him knowing. The fate of the planet will depend on Darren stealing it back. The Grubs send a second musical countdown message to announce their arrival in eight days.
The Moonlings deliver a cold fusion reactor to the Mellop kids, and with the molecular exciter back in their hands thanks to Darren, the Woop is restored. Jason uses the window to travel to the Opera House to snap some reference photos. Sam tries to demonstrate the Woop for her father but he is too distracted by Dump's argument with Mr O'Neill to see. Things are beginning to fall into place with just the model of the Opera House left to complete. Michael suggests Sam get aunt Jocelyn to finish it. As a precaution Sam doesn't want anyone else using the Woop but Michael asks for Ebony's help to determine the Woop's power reserve level. Darren uses the Woop.
Sam's father is growing increasingly concerned about her "crazy stories". Darren has delivered the Woop window to his uncle who is using it to start an airline. Dump even secures a bank loan after demonstrating the device for his banker. Reluctantly agreeing to let Dump keep the window until they need it, the kids get Dump to let them check the power level of the Woop as they are concerned about how long it will run with Dump using it. Jocelyn begins building the Opera House model believing she is helping Sam with a school project. After receiving the Grubs' third countdown message, the kids decide to get Dump's rival, Mr O'Neill, to help them recover the Woop.
Jason recruits Mr O'Neill to help recover the Woop by framing it as a chance to get back at Dump for killing his flowers. Despite Dump's ban on anyone associated with the Mellops from using the Woop, a disguised Mr O'Neill makes it through the window portal back to the Mellop residence but, as anticipated by Samantha, he lands squarely on top of aunt Jocelyn's nearly complete model of the Opera House. Meanwhile, the Woop dumps Dump out in woop woop. Royal Dump Air attracts the attention of the media but with Dump nowhere to be found, it is dismissed as a hoax which upsets Dump's bank manager who has funded the endeavour.
With Dump abandoned in the middle of the outback by Mr O'Neill, Sam reaches out to Darren to let him stay at her house until he gets back. The Grubs send another musical countdown message but they've skipped a number — they'll arrive in five days! Darren goes online to the galactic bulletin board and discovers the Grubs' home planet is on the other side of the galaxy which is outside the range of the Woop. It will be impossible to deliver the Opera House model and save the world!
Michael theorises that with a stronger power source their Woop might be able to reach the Grubs' planet. Ebony helps them contact Planet Peaceful, which is easily in range, to see if they know what power source the Grubs use. The kids draw straws to see will make the trip with Sam and Michael selected to go while Darren and Jason staying behind to finish the Opera House model. The kids leap through the Woop, but Dump, who was outside the house, is pulled along for the ride along with the Mellop's dog. Aunt Jocelyn searches for the owner of the paint-covered shoes that damaged her grand reopening banner.
Sam and Michael take the Woop to the Grubs' spaceship leaving Dump behind on the surface of Planet Peaceful to make his own way there. They kids access the ship's library where they find a manual for Woops but are cornered when a Grub arrives. Jason covers for his siblings absence and fixes Jocelyn's banner. In London meanwhile, one of Dump's stranded airline clients is beginning to draw the attention of the media.
Cornered in the Grub library, Sam and Michael are able to escape with the Woop power source information after Dump triggers an alarm elsewhere in the ship. On the run from the Grubs, Dump stumbles across the Woop window and takes it back to Earth leaving Sam and Michael trapped on the Grub spaceship. Sam and Michael are able to send a fax back home to Jason asking for help. Bill reads the message that says Dump left without them and goes to Dump for answers. When Dump tries to show Bill the Woop window, it is gone.
Dump tries to keep Bill from panicking about his kids, promising to get them back after he gets "his" window back. Darren offers to help Jason fix Jocelyn's banner which is only getting worse. While waiting to be rescued, Sam and Michael have the idea to fax the power source information to Jason. To supercharge the Woop, he'll just need to find a compressed sun. Dump suspects Fabian, his dog, has taken the Woop somewhere, possibly to London, where Dump's stranded customer, Sir Ian, has developed a fanatical following. Darren offers to help Ebony fix her clock using the Mellop's kitchen clock for reference. He also finds in the kitchen… the Woop window.
Darren wants to prove just how good a friend he can be by taking the Woop to the Grubs' spaceship to rescue Sam and Michael but cannot muster the courage. Jason comes home and makes the leap without a second thought. Tired of waiting, Sam and Michael decide to return to the library but are spotted by one of the Grubs. They are pursued through the spaceship until they run into Jason. Back on Earth, Bill calls the police but when they enter the house to discuss the missing kids, there they are, safe and sound. The kids reassure their father that they'll be there for the grand reopening of the nursery — just as soon as they find a Black Hole. After Darren is forbidden from talking by the Mellop kids, Dump tries to coax him into revealing what he knows about where a Black Hole can be found.
Under tickle torture, Darren reveals to the Mellop kids that Ebony lives in a Black Hole. Working together, the Dumps and Mellops ask Ebony if she has a compressed sun to give them. She does but according to its instruction manual, they'll need an antimatter paper bag to get it out of the Black Hole. The Grubs send the next number song counting down to their arrival. Dump uses the Woop to pop over to the antimatter universe where he runs into a strange version of the Mellop family. He returns with the antimatter paper bag — and the other Mellops who must be keep away from Bill and Jocelyn so they don't all blow up in a matter-antimatter explosion!
Dump attaches the antimatter paper bag to Bill's prize-winning orchid and sends it through the Woop to Ebony who puts in the compressed sun and sends it back. Dump next whisks the antimatter versions of Bill and Jocelyn to the safety of his caravan. While the pair hide out at the nursery, Michael and Sam check in on Dump only to learn he's taking his time in saving the world. Forcing him to deliver the Opera House model, Dump drops it off with the Grubs and returns home to begin marketing his Woop. He's willing to send the other Bill and Jocelyn home — for a price. After polishing off the Opera House model, the Grubs decide to break their promise and continue to Earth to throw a party and eat the real one.
The Grubs are divided between those who want to continue sending musical faxes and those who want to speed their arrival to Earth to start partying. With the compressed sun in his possession, Dump brainstorms ways to capitalise on it's instant, unlimited energy. He settles on a pizzaria — your pizza in two seconds or less. The kids promise to give Dump a million dollar idea if he takes the "antis" back home to the antimatter world. He does but the kids then have to admit there's no idea. Darren wants to fix Ebony's clock as he promised but keeps getting put off. Just when it seems all is right with the world, the Grubs' latest countdown fax arrives — they are three days away!
A new threat to the Earth emerges — the antimatter fertilizer pellets the anti-Jocelyn gave the nursery plants. Michael rushes to the nursery to separate the antimatter pellets from the matter pellets while Sam and Jason try to distract their father. It doesn't work. The molecules of the two pellet types interact causing the plants to explode leaving the nursery a shambles. The Grubs' eighth message arrives. With the nursery reopening looming, Jason tells his father he's arranged for the gala to be covered live on TV by Dr Ken who he's promised will see "the greatest show on Earth". To save the Earth, Sam decides their only hope is to teach the child-like Grubs the difference between right and wrong. The kids are desperate to get their hands on the Woop to go visit the Grubs only to learn Dump has taken it to London for five days to drum up interest in his new tanning business.
Sam calls London to plead with Dump to bring the Woop back but he's not willing to cooperate having found some eager customers. Darren tries to help Ebony fix her clock which somehow triggers an Earthquake that breaks the Grubs' hourglass. Despite the loss, the Grubs send their ninth message counting down the remaining minutes until they arrive. Darren asks Ebony if she can leave the Black Hole to come for a visit. She doesn't know, is even uncertain of how she got there, but knows she is waiting for her friends to arrive. Help arrives out of the sky in the form of a flying dog kennel — Jane and Ralph have returned from the moon!
Jane takes Sam and Michael to London in the dog kennel where Ralph has already stolen back the compressed sun Dump was using to power his tanning business. Sam and Michael use the Woop to travel to the Grubs' ship where they accidentally disable the Grubs' countdown timer. Jane flies Darren to London to rescue his uncle who, now revealed as a fraud, is besieged by angry customers. Sam and Michael appeal to the Grubs to grow up and start acting more responsibly. Darren finally helps Ebony fix her clock, he suggests all it needs is a good thump.
The sudden appearance of a tree on planet Gruble forces the Grubs to keep their promise to try growing up. Back on Earth, the "greatest show on Earth" is taking shape but Bill isn't impressed by Jason's dance number with Jane and Ralph. Darren uses the Woop to send Ebony a note attached to a rose asking if her clock was fixed. He anxiously awaits a reply that doesn't arrive — but Ebony does. Sitting on the porch she explains how Darren helping her fix the clock was the key to stopping the Grubs. Restarting it was what caused plant growth to restart on planet Gruble and was what allowed her friends to grow up. Her friends the Grubs.
