We are in the year 2037. Mankind is threatened with extinction after a nuclear war and epidemics. Mankind is governed by barbarians, who are opposed by cloned scientist, who try to breed some new kind of human to help them fight the government. The scientists have some trouble though, because these test-tube super-humans have a tendency to be just as uncalculable as normal humans. We are told all this, while one of these new super-humans, a little boy, is driven to the headquarters of the scientists.
The little boy is Matti, the special project of a scientist of the Jürgen-clone, called "Doctor". After greeting Doctor, Matti sits down at a console to get involved in a game, which he seems to play in order to practice for his future part in fighting the government troops. A talking, thinking giant truck, a la Knight Rider, called "Monster" is driven by the girl Gus. Monster is programmed and fed information by Matti. Gus and Monster have to make their way to some mysterious goal past all kinds of obstacles and government troops, also called "the greys". In this first sequence with monster, they get trapped in a village by the greys but in the end manage to break through. Matti gets applause from the scientists standing around him and watching the game.
Doctor reports to the head of the Jürgen-clones, a red-wigged creature referred to as "sir". Sir is not pleased with Matti's performance, he doesn't trust him, because he is too intelligent and unpredictable. Doctor still believes in Matti.
Meanwhile, Monster and Gus have entered an area, where they are not supposed to go in the game. Matti insists, that this is not his fault but that Gus made this decision. Monster is stopped at a roadblock of the government troops. After a fight, Gus is taken prisoner and brought to a fort of the greys. In her cell, Gus meets a fellow prisoner, Stump. He has an artificial hand since he tried to resist the government. They fall in love and Gus tells Stump in a hidden way with her matches the password for driving Monster : "If you have to chose between the flame and the light, chose the light."
Gus is taken for interrogation and tortured by the soldiers. Before she dies, she can tell a little servant girl, called "Princess", to give the message to Stump, that he has to get into Monster and continue the journey. Princess helps Stump to enter Monster and Stump, remembering Gus, says the password without knowing what he is doing. Monster makes plans for their flight and they manage to get out of the fort.
Matti and Doctor call up information about the new driver, who is a rebel, we are shown some scenes, how he got the metal hand. Doctor doesn't trust him, but Matti is convinced, that he must be all right, if he knew the password and Monster accepted him.
Monster tries to explain to Stump the game, that Matti developed but claims not to know yet, where the exact goal is. He only knows, that it is far away in the west. After their flight from the fort, they are followed by government troops. When they reach a rather dilapidated bridge, Stump manages to damage the bridge in a way, that most of the soldiers crash through.
Princess has come along as a passenger and Monster has stored information about her: she was one of the would-be-superhumans of the Jürgen-clone, a failure, who ran away and ended up as a servant girl in this fort, where she was again mistreated. Stump doesn't mind taking her along, he is depressed by all the misery Princess, Gus and himself have experienced. They break through another roadblock at a border but Stump doesn't trust Monster, he doesn't hand the driving over to the autopilot. He takes Monster to a garage in a city, which seems to be Sodom or Gomorrha and where, of course, they are not supposed to be.
Matti and the scientists could watch these developments. Red-wig Sir has come to the conclusion, that Matti is a failed experiment and that this game has to be ended before it gets completely out of hand. Doctor obeys and calls "Little Brother", who is the Jürgen-clone responsible for the rough and dumb work. (The most familiar looking of the lot.) Little Brother also goes hunting for Monster, in another big truck, which has the advantage of being able to make itself invisible.
Meanwhile Stump in the garage in Gomorrha has found Monster's brain, a little silicone ball. He threatens monster with destroying his brain. Now Monster confesses, that Princess and Matti are siblings. Princess turned out to be too human and was to be destroyed, but managed to run away. Matti was not much different but pretended to be cold and monster-like, he also invented the game in order to appear inhuman. In reality, Monster has been programmed and equiped to save Princess and get her back.
When Doctor realizes, what is happening, he leaks information to the greys, who catch Stump and take him for interrogation. But Princess and Monster manage to save him and all their government pursuers have nasty accidents on the autobahn. There is still the ghost-truck, though, with Little Brother steering it. They materialize, while Stump and Princess have a rest after the chase, and turn over Monster. Stump has to fight Little Brother and wins. Little Brother has the key to the ghost-truck on a string around the neck. As Julie already observed, Stump drags the whole Little Jürgen along in order to open the truck. I can only suggest, that he just felt like dragging somebody over rough ground. Inside the truck, a shock awaits Stump, the secret behind Sir's experiments: this truck hasn't got a silicone brain, it is powered by children!
Stump blows the whole horror-truck up and this seems also to kill the red-wigged Sir. Doctor and his colleagues leave headquarters. They want to take Matti, but he threatens to tell the government their location. They leave him behind.
Matti guides Stump, Princess and Monster on the last part of the journey. In the end, he is reunited with his sister. Stump says "We (the unpredictable humans) have won after all!"