Fifteen-year-old Daniel X is a highly intelligent alien with superior strength and speed. He has the ability to create and transform objects, teleport himself from one place to another and travel through time.
Daniel is also an alien hunter, following in his parents' footsteps by tracking down a list of alien criminals on Earth. He ultimately wants to kill No. 1 on "The List of Alien Outlaws on Terra Firma" — The Prayer — the alien who murdered his parents and burned their house to the ground when Daniel was a toddler. Dana, Emma, Willy and Joe are Daniel's childhood friends, who were all killed during an alien invasion on his home planet of Alpar Nok. He conjures up his family and friends with his ability. His parents give him advice, and his friends come to life.
Daniel has traveled to England to find the third most wanted alien on The List: Phosphorius Beta from the volcanic planet Cyndaris. Beta's body is composed of fire; he can manipulate flames and control human minds and bodies. Daniel's loved ones caution him about going after Beta due to the alien's immense power and Daniel's fear of fire, which stems from the day his parents were murdered.
On the way to London, Daniel and his friends stop to play soccer, and afterward, Daniel is too tired to materialize transportation for the group. When an old lady in a van offers them a ride, they gratefully climb in, but Daniel soon realizes that they have been tricked by No. 43 on The List, a shape-shifting alien. The van is a part of the alien's body.
As Daniel and his friends are about to be eaten, he hears his father's voice reminding him that he still has time to take out No. 43. Remembering his ability to turn back time, Daniel returns to moments before the van arrives and then destroys the van. After this incident, Daniel becomes increasingly worried about his friends' safety and vows to never let anything happen to them. His mother reminds him that his friends are already dead, and he can always conjure them up again, but that reminder does little to alleviate Daniel's fears.
In an abandoned London townhouse, Daniel and his friends watch a news report of an explosion and see a black shape with eyes and teeth take form in the fire. They realize that the fire is Beta, and he is responsible for the destruction.
The group decides to split up and investigate the industrial areas of the city where fire is most prevalent. On their way to a metal foundry, Daniel and Emma see a large man following them. They hide, and when he heads back to his apartment, they follow him.
The man turns out to be one of Beta's followers, a human to whom Beta has given the power to project fire from his eyes. (The group dubs him "The Cockney Fireman" due to his thick accent and burn marks on his body.) When the man sees Daniel, he attacks him with fire. Daniel and Emma escape, but Daniel is burned.
The two return to the townhouse, but Daniel finds it hard to rest because he is fearful of his friends being in danger. When he finally falls asleep, he dreams that his father takes him to a place that mimics the conditions on Cyndaris and puts him through a vigorous training. Daniel's father tells him that strong emotions and powerful events can cause stress points in time through which Daniel can travel, but warns him not to abuse this powerful ability to manipulate time.
A few days later, Daniel breaks into The Cockney Fireman's apartment, but The Fireman arrives and causes the room to erupt in flames. The Fireman's body then bursts into flame, and Phosphorius Beta appears. Daniel tricks Beta into falling off the apartment's balcony and into the swimming pool below. Beta disappears into a cloud of steam.
Daniel returns to the metal foundry only to find that Beta is still alive and controlling humans. Daniel sees Beta's followers loading metal parts into a truck, so he turns himself into a steel bar, joins the other pieces of metal and travels to Beta's headquarters, which is an enormous junkyard filled with bonfires and hundreds of Beta's human followers.
Much to Daniel's surprise, Dana shows up, and the two hide in an abandoned car. They see a massive Cyndarian space ship filled with plants and animals being sent to Beta's home world as fuel. When Daniel realizes that Beta has sensed them, he tries to teleport out of the car but is too stressed out to focus.
Beta finds them and sets the car's exterior on fire, which rattles Daniel even more due to his fear of fire. After trying and failing at teleportation and transformation, Daniel tries time travel to escape the burning car. Since emotion is the switch that allows time travel, Daniel kisses Dana.
Just when he thinks he will burn to death, he opens his eyes to find himself lying in front of his childhood home on the same day his parents were killed. When he hears gunshots, he realizes he is too late to save his parents. But Daniel's father has time to warn him about The Prayer and tell him to look around. When he does, Daniel notices a time portal and steps through it, landing in medieval England, where he meets young Arthur Pendragon and his tutor, Merlin the Wizard.
Merlin recognizes Daniel as an alien because Merlin is also an alien hunter from Alpar Nok assigned to Earth. When Merlin shows Daniel his version of The List, Daniel realizes he has traveled back to the time when Beta originally arrived in the British Isles. Merlin takes Daniel to a lake, where they see a flame exit a time portal and disappear into the woods. It's Beta, and Daniel wants to pursue him, but Merlin tells him to be patient and wait for the right moment.
The next day, Merlin takes Arthur and Daniel to London. Once there, the boys see a crowd forming around a sword in a stone. A man announces that whoever pulls the sword out will be king of all England. Daniel takes a closer look and realizes that Merlin has transformed himself into the sword. Telepathically, Merlin tells Daniel to encourage Arthur to try for the sword. At first, Arthur is reluctant, but he gathers his courage and pulls the sword out of the stone.
That night while everyone is celebrating the newly declared king, Daniel follows a man suspected of being in league with Beta to caves just outside of town. Beta is in the caves and has taken the form of a large dragon. As Beta and Daniel battle, Arthur shows up in the cave with Merlin in sword form. Telepathically, Merlin tells Daniel that it is Arthur's job to stop the dragon.
Once again, Daniel helps Arthur be courageous by encouraging him to fight Beta. Beta tries to burn Arthur, but Merlin drops the temperature so Arthur can thrust a frozen sword into Beta's side, killing the dragon. The few sparks that are left of Beta jump out of the dragon's mouth and disappear through a fissure, so Daniel knows it is just a matter of time before Beta rises again.
Merlin explains that Beta has been tormenting human civilizations as some form of fiery beast for thousands of years, and that his alien hunter mentor, Guinevere, built Stonehenge as a machine to stop Beta. While Guinevere never told Merlin how Stonehenge works, she did say that the key to destroying Beta was to look to the sky.
Armed with this knowledge, Daniel returns through the time portal Beta created on the lake and reappears in the junkyard. He finds Dana, who had also been sucked into the time portal. After Daniel leaves a note in the junkyard telling Beta to meet him at Stonehenge the following night, the two escape.
At Stonehenge with his friends and family, Daniel nervously waits for Beta, because he doesn't know how the structure works. Before long, a convoy of trucks driven by Beta's followers arrives. Fire begins to pour out of the trucks, and the flames join into a tall, orange column of fire, which is Beta.
Beta tells Daniel that when he was forced underground during the Dark Ages, he had time to rethink his methods. Instead of burning a few houses himself, he now has a huge, villainous army to do it for him. He now concentrates on sending things from Earth back to Cyndaris as fuel.
As the fight ensues, Daniel is injured with third-degree burns and begins to run out of battle strategies. Then he notices that Stonehenge is glowing red from Beta's heat, and the sky is red with the approaching dawn. He also remembers that Merlin told him to look to the sky.
Suddenly, Daniel realizes that even in its ruined state, Stonehenge is acting like a giant lens focusing the sun's heat into a single intense point. The heat is attracting Beta like a magnet, and his column of fire reaches high above him. With a loud sound like a thunderclap, Beta's flame shoots toward the sun, the one fire that not even he can handle.
As the alien hunter bids good riddance to No. 3 on The List, and Beta's minions struggle to recover from being possessed, Daniel realizes that Stonehenge has finally completed its task: saving England.