Toaster is the leader of a gang of appliances consisting of a radio, a lamp named "Lampy," a blanket named "Blanky" and a vacuum cleaner named "Kirby," who belong to their "master," a young boy named Rob. They wait every day at Rob's cottage for his return with an increasing sense of abandonment, which causes Blanky to hallucinate about finally seeing Rob coming back. On the second day of July, the appliances are devastated to learn that a real estate broker is selling the house. Not wanting to accept the fact that the Master would abandon them, Toaster decides that the group should head out and find Rob. The appliances connect a car battery to an office chair pulled by Kirby and set out into the world, following Radio's signal broadcast from the city where Rob has moved to.

On their journey, the appliances encounter numerous harrowing adventures where they learn to work together. Shortly after stopping to rest within a forest, a nightmare where Rob and Toaster get tortured by an evil smirking clown dressed as a firefighter followed by a violent storm during nightfall wakes Toaster and the others with the storm blowing Blanky up into the trees, and Lampy risks his life by using himself as a lightning rod in an attempt to recharge the group's dead battery. After recovering Blanky the next morning, they try to cross a waterfall, but during an attempt to cross it, everyone falls in except for Kirby, who dives after them and rescues them, and the appliances wash up into the middle of a swamp. After losing both the chair and the battery, the group resorts to pulling a disabled Kirby through the swamp. After losing their balance and almost drowning in a mud hole, they are rescued by Elmo St. Peters, an owner of a spare parts shop, where they get scared by a group of partially dismantled or disfigured appliances, who have lost hope and are at risk of being disassembled or sold, almost in a prison-like motif. When Radio is removed from a shelf and about to have his radio tubes extracted, the appliances frighten St. Peters by pretending to be a ghost and flee to the city, while most of the worn-out appliances flee the store and return to their masters' homes.

Rob, who is now living in a modern apartment as a young adult and is about to depart for college, leaves with his girlfriend Chris to return to the cottage and retrieve the appliances to take with him. After secretly witnessing this, Rob's newer appliances in the apartment become resentful. When the appliances arrive at Rob's apartment, the newer appliances explain that they are "on the cutting edge of technology". After answering Toaster and the other four appliances their question of what they mean by singing their song to them, they kick them into the apartment's dumpster from the window, where they are shortly transported to Ernie's Disposal, which is a junkyard. Thinking that the cottage has been broken and trashed and his original appliances were stolen, Rob and Chris return to his apartment, where a T.V., who is another appliance owned by Rob, broadcasts false advertisements to encourage him and Chris to go to Ernie's Disposal to find Toaster and the other four appliances and bring them back.

At the junkyard, the appliances are tormented by a maniacal crusher with its henchman, an evil tower crane with an electromagnet that picks up junk and places them on its conveyor belt that leads to the crusher. When they discover that Rob is in the junkyard, they are encouraged that he still needs them after all, and then, they attempt to foil the magnet in order to allow Rob to find them. After being foiled numerous times, the magnet decides to pick up Rob as well as his appliances, and drops them on the conveyor belt. Toaster makes a heroic sacrifice by jumping into the crusher's gears to disable it just in time to prevent it from killing Rob and destroying his appliances. Rob survives and returns to the apartment with all of the five appliances in tow, including a mangled Toaster. And then, Rob repairs Toaster and takes the five appliances with him to college, along with Chris.

Rob and his girlfriend Chris have married and now have a baby son named Robbie who plays with Toaster, Blanky, Lampy, Radio, and Kirby just like his father did when he was little. The appliances make it their prime directive to make sure nothing happens to Robbie to which they refer to as the Little Master. That night the Hearing Aid, who was left in the junk drawer by his former owner, Albert Einstein, sneaks out and goes to the window and gets in contact with someone from space telling them that tomorrow night he'll be ready. Toaster who has secretly followed Hearing Aid listens from behind the door and tells the others the next day about Hearing Aid and decide to keep an eye on him but as night falls they fall asleep on the job. Hearing Aid sneaks out again and goes to the window and gets in contact to the aliens which they call Robbie, who decided to be getting himself.

Robbie is the first to appear at the window and while the appliances fight off Hearing Aid, Robbie gets transported into space. The appliances learn that Robbie has been transported to the planet Mars and Hearing Aid said he was supposed to get transported to Mars and volunteers to accompany the gang to go to Mars and rescue the Little Master. The gang contact their old college buddy Wittgenstein through the computer and he gives them the equipment they need they need to get an overhead fan named Fanny to fly, a laundry basket to travel in, a microwave oven and microwave popcorn with cheddar cheese flavoring to help them fly. After getting all the stuff they need the appliances head off to Mars and on the way they're encountered by singing balloons. Once they get to Mars the appliances are greeted by numerous big and small machines, including Viking I the Satellite, Tinselina the ACAM and the Wonder Luxe Appliances who had built a rocket ship and landed on Mars after their owners on Earth threw them out.

The appliances show that they have Robbie as their special prisoner and plan to destroy Earth after being hurt for being thrown out. Toaster tries to talk them out of it but is put in an Election with the leader, the Supreme Commander, who is Hearing Aid's twin brother controlling the Giant Refrigerator as his disguise, but when Robbie touches him, he learns that not all humans are bad and decides not to destroy Earth after all. That night Hearing Aid is reunited with the thing who he got in contact with who is the Supreme Commander revealing his real self. The next day the appliances along with Hearing Aid's brother and Tinselina depart to leave to go back home to Earth but as they are about to fly off Hearing Aid's brother forgot to stop the Missile and he and Toaster rush back to the Missile and stop it just before it is about to destroy Earth. Toaster at first is happy because they managed to stop the Missile but is also sad because he thinks that he and Hearing Aid's brother are getting left on Mars but the gang manages to come back and rescues them and head for home. As soon as they get home Robbie walks into his room to his parents who think that he learned it in the night. Soon it's Christmas and Robbie says his first word which is "Toaster!" And he brings in Toaster, Radio, Blanky, Lampy, and Kirby to which Chris turns to Rob and says, "Like father, like son." While Chris and Rob leave the room for a little while the gang comes alive and celebrates Christmas with Robbie and look up at Tinselina who Rob and Chris put up on the top of the tree.

Rob McGoarty is working in a veterinary clinic where he tends to injured animals. One night, while working on a thesis, his computer accidentally crashes due to being caused by a terrible computer virus from an old TLW-728 prototype supercomputer named Wittgenstein. The appliances, along with the rat Ratso who found Wittgenstein, then seek to help Rob by finding Wittgenstein to reverse the effects of his computer virus, hence recovering the master's thesis. Meanwhile, in a dual plot of the film, Mack, Rob's lab assistant, plots to sell the injured animals Rob had been tending to as part of his courses to a place called "Tartarus Laboratories", the same place that Sebastian, an old monkey Rob is tending to, was sent to when he was just a baby. When the appliances find Wittgenstein, they discover him abandoned, all alone and run-down and broken in the basement due to being infected by a computer virus, the same one that affected Rob's dorm room computer and the one in the vet clinic's lab when Wittgenstein try to contact them earlier. The miserable supercomputer reveals that he is living on one rare vacuum tube, named the "WFC 11-12-55". The name of the tube is a reference to the producer and screenwriter, Willard F. Carroll (WFC), and his birthdate, November 12, 1955 (11-12-55). The appliances learn that unless they find a replacement quickly, Wittgenstein's tube will blow and lead to his apparent death.

In an attempt to revive Wittgenstein to his superior state, Radio and Ratso go to the college's storage building to find the hard-to-find WFC 11-12-55 tube. When they come back with the last apparent tube for miles, however, Radio and Ratso (after an argument with the tube) accidentally break it, and it seems that all hope is lost. Wittgenstein does his best with all his might, but the virus causes him to blow his remaining tube with a big explosion and apparently "is a goner". Ratso then blames Radio, and guilt-ridden over condemning the animals to their doom at Tartarus Laboratories, Radio gives up his own tube which turns out to be the very rare tube they had been looking for, thus killing himself. Knowing that they were given a final chance to save the animals, the appliances replace the tube in the nick of time. With the boosted power of the new tube, Wittgenstein wakes up, miraculously regenerates the other smashed tubes connected to himself, and destroys the computer viruses within him, allowing him to be completely revived to as good as new. By the end of the film, the appliances restore Rob's thesis and stop Mack from selling the injured animals and have him arrested with some help from Wittgenstein, Rob and his girlfriend Chris (later referred to as "The Mistress"), two guard dogs, and the police. After discovering the appliances in the truck, they assume that Mac had also planned to sell Rob's stuff as well, although Rob is surprised that Radio isn't here. Later, they discover Wittgenstein in the basement along with Radio. Later, Radio's tube is replaced with a new one Chris found in Nome, Alaska (hence his revival), Wittgenstein is sold to a museum and will be modernized with current technology, Rob proposes to Chris, and all is well.