Drew Carter is the new kid in school. He is smart and muscular with a talent for football. His dad was killed while in the Army Special Forces when he was 12, and now Drew and his mother, Kathryn, are starting a new life in a small Kansas town. Drew's dad served in the military alongside Jake Blanchard, his best friend.
Jake keeps an eye out for Drew and Kathryn. He befriends Drew and his mother and encourages Drew to join the football team, go with him on camping trips and learn survival skills. The camping trips take Drew to many unique places around the world, and over time, Jake expands his instruction to include martial arts and combat skills.
Drew befriends geeky Benjamin Berg, the assistant for the football team. Ben is a genius who aspires to be a physicist, and he believes alien life forms exist and religion serves as a crutch for the weak. Drew isn't sure what to make of Ben's alien theories.
Drew is attracted to a girl the other guys call "church chick." He finds out in speech class that her name is Sydney Carlyle. Drew tries to get to know her better by asking her out, but she tells him she doesn't date.
After one of the football games, Drew attends a party at another boy's house. Beer is available. Drew succumbs to peer pressure and accepts a beer. He has a few sips, and then pours it down the drain. Uncomfortable with the scene, he decides to leave, and three of the other boys from the team decide to ride with him since they'd been drinking. As Drew enters an intersection, he hears a beer can open and turns to chastise the boy in the backseat. At the same time, a pickup comes through the intersection, broadsiding Drew's car and killing Joey, the quarterback, in the front seat.
Drew survives physically unharmed, but his transition back to school after a 10-day absence is difficult. Ben is there for him though, and he helps him regain his footing, emotionally and academically. Sydney becomes a little more open to Drew for conversation. She and Ben are the only two at school he talks to. The next year, Ben goes on to Drayle University and convinces Drew, now a senior, to apply for an academic scholarship to Drayle.
Drew is accepted to Drayle, and once he leaves for Drayle, he is happy to put his past behind him. Ben stays busy helping research professor Waseem's theory that an alternate dimension exists using LASOK (laser light acceleration technology). To his surprise, Drew discovers that Sydney is also a student at Drayle. They meet once for coffee, but Sydney breaks off further meetings since Drew is not a Christian, and she is. Drew and Ben grow to be close friends, meeting weekly to catch up over coffee.
One day, Ben tells Drew that Waseem is missing. He says that Waseem learned that one of his experiments using the LASOK succeeded in seeing into another dimension. Waseem left behind some photographs for Ben as proof that dark forms are present, but can only be seen through the LASOK lens. They think the dark shapes are aliens, or perhaps invaders. To prove that it's not all a hoax, Ben and Drew determine to repeat the experiment that night. Their experiment goes awry, ending with an explosion, but not before Drew views a dark, evil invader in the room through the LASOK lens. Drew's world goes black, and he awakens in a hospital unable to see but with all of his senses heightened.
The university expels Ben, holding him responsible for destroying the multimillion-dollar lab. Drew drops out of school to recover from his injuries. He and Ben learn that Waseem has died a suspicious death. Ben visits Drew once to discuss the dark invader that Drew saw, then tells Drew that he plans to disappear. They assume there is more than one invader, and they fear for their safety.
After several months, Drew's vision slowly returns until it eventually improves to better than 20/20. His energy is limitless, and his senses are heightened — he is no longer an average human. One morning, he stops at a grocery store, and while he's there, he sees more invaders. They are evil-looking, wear black and are armed with swords and guns. Drew realizes the explosion has left him able to continue to see into the alternate dimension, and he is more afraid than ever. He knows he has to find Ben so they can plan a counterattack against the invaders. Ben is the only one who will understand what he's coping with.
On a camping trip with Jake, Drew reveals what has happened, thinking Jake is someone he can trust. But Jake later shares the information with Kathryn, who calls in a psychiatrist. Drew feels betrayed by Jake and hurt by his mother. He flees his mother's home in anger. Jake tracks him down, apologizes and provides Drew with a few thousand dollars and a second ID so he can go off the grid to find Ben and deal with the invaders that only he can see. Drew returns home to his mother, and they reconcile the night before he plans to disappear.
The next day, before he goes off the grid, Drew decides to stop at Drayle to say goodbye to Sydney. After he leaves Sydney's classroom, he is alarmed to see more of the evil invaders. He notices that they are influencing a young man armed with an MP5 submachine gun. He fires into a group of students. A girl is shot in the leg, so Drew carries her up the stairs and into Sydney's classroom for cover. Drew, Sydney and about 30 other students are trapped as an invader passes through the door, soon followed by the gunman.
Drew locks eyes with the invader, and now he knows that they know he can see them. Suddenly another invader comes through the window, but this one is wearing white. Drew watches as the two invaders fight, with the one in white triumphing over the one in black. The one in black vaporizes as he dies. Drew tackles the gunman, knocking him unconscious, and the other students secure him. Drew is mystified to see a blue glow around Sydney as they sit and wait for law enforcement to show up.
Intent on disappearing so he can begin his search for Ben, Drew flees the campus on foot since police are watching all the cars leaving after the lockdown. He knows the FBI will handle this disaster and that they think he's somehow in on the shooting, so they'll be searching everywhere for him. He heads for the bus station where he buys a ticket to Des Moines to start his search for Ben.
He sees more dark invaders manipulating a man to harm a little girl at the station, and again a light invader comes to the rescue. Drew's bus finally leaves, but one of the dark invaders gets on the bus, too, watching Drew for the duration of the trip. Drew buys another ticket to Duluth, and the invader follows him. From Duluth, Drew hikes for days into a forest near the Canadian border with the invader still following him. Drew finds that Jake had prepared him well for survival on his own.
The invader attempts to control Drew's mind, prodding him toward fear and thoughts of suicide. Worn down by the dark invader's harassment, Drew decides to jump into a frigid lake and swims along the shore. He is surprised to find that the dark invader will not enter the water. The close proximity of his enemy has given Drew an opportunity to study and learn about this dark force.
Eventually, Drew senses his dark burden lifting, and when he looks up he finds the invader gone, but only for an hour. When the invader returns, he sets about tormenting Drew and causing multiple things to go wrong. Eventually, Drew evades his tormentor and makes his way to Chicago where he is certain of seeing more invaders and hopeful of finding Ben.
Drew gets a tiny apartment in the inner city. Weeks have passed in Chicago, and Drew is no closer to finding Ben. During the day, he visits computer repair shops, hoping to find the place where Ben is working.
On a walk to the grocery one night, Drew defends an old homeless man from four thugs. One of them shoots Drew in the shoulder. After they flee, the old man asks Drew to take him to Emmanuel Church to see the Rev. Ray. The reverend takes them in, and he and his family minister to them, cleaning their wounds and feeding them. Drew learns that Ray runs a soup kitchen from Emmanuel, and Drew decides to volunteer there once a week.
He continues to go out at night looking for people to help. Several times, light invaders come to his rescue. His finances draining, Drew asks Mr. Lee for a job delivering Korean food. Mr. Lee tells him no car, no job. Drew notices a martial arts certificate on Mr. Lee's wall, and challenges Mr. Lee to spar with him for the job. They meet that night at Mr. Lee's Tae Kwon Do school. Mr. Lee first has his assistant spar with Drew, then spars with him himself. Mr. Lee is impressed by Drew's speed, and he tells him he will train him three nights a week. He gives Drew the delivery job, permitting him to use his own car for the deliveries. Mr. Lee somehow understands that a darkness follows Drew, so Drew reveals some of what has been happening to him so that Mr. Lee will continue to train him. Dodging bullets is one of the skills he wants to (and does) learn.
One evening when Drew shows up at the church, Ray tells him a group of volunteers from Drayle Campus Ministries is there to teach vacation Bible school and help at the soup kitchen. Drew is excited to see Sydney in the group, but he doesn't want her to see him since he is off the grid and under a different name. He fears that either he will endanger her or that she will blow his cover.
Light invaders guard the church, ready for an attack by the dark invaders. A big battle ensues between the light and dark invaders as the volunteers get into their van to return to their hotel. Under the influence of the dark invaders, the van gets a flat tire a few blocks from the church, deep in the turf of a gang called the Dragons. Drew follows on foot, watching from a distance. The Dragons waste no time in robbing and threatening the students. When Drew sees them pull Sydney and another girl aside, he enters the conflict and fights with the Dragons.
Drew has already earned a reputation in the area for his feats of valor. The locals refer to him as the Guardian, and some of them fear him. A fight ensues, and a light invader intervenes to save Drew when one of the Dragons aims his gun at Drew's heart. The Dragons run away as police begin to arrive. Drew escapes and sees the light invader who saved him leaning against a building, seriously wounded. Drew approaches him, wanting to help somehow. The invader even materializes into Drew's world to warn Drew that he must go before the authorities find him. Then the invader, whom Drew nicknames Wallace, returns to his realm, and another light invader arrives as Drew departs.
The next day, Drew returns to the church and is surprised to see that 13 light invaders stand guard and that the college students have returned. He's not sure if they're brave or stupid. That night he goes to Sydney's hotel to explain some of the issues he's dealing with. He remains vague about the alternate dimension he can see because he doesn't want Sydney to think he's crazy, and he wants to protect her. She surprises him when she tells him there are unseen forces at work in this world.
Drew cuts short their conversation when a group of dark invaders suddenly appears. He evades them for the moment and ensures that Sydney safely reaches her hotel. The college kids return to Drayle a couple of days later, and Drew finds he really misses Sydney. The next time he goes to Emmanuel, Ray introduces him to a new volunteer who turns out to be Sydney. She tells Drew she is transferring to the University of Illinois in the fall and rooming with her cousin, and she is now available to help him search for Ben.
They finally manage to locate Ben, who is besieged by dark invaders intent on ending his life. Drew and Ben evade numerous dark invaders until they reach a lake outside the city and rent a canoe to get out on the water where they are safe from the dark invaders. Together they formulate a plan.
In order to get help from others, they need convincing evidence, and the only way is for them to reconstruct Waseem's experiment with the LASOK. Ben happens to have Waseem's work backed up on his hard drive, so all they need are funds. Drew spends weeks sharpening his trading skills for the mercantile exchange, and little by little he acquires the money they need for the project.
Drew at last feels compelled to be completely honest with Sydney, and he tells her everything. When she leaves without saying anything, he and Ben are afraid she'll inform the FBI, so they decide to quickly pack up everything and find a new location. Before they finish, Drew gets a text from Sydney indicating that Ray is in big trouble with the Dragons.
Drew drops everything to go and help. He arrives just as an ambulance is taking away Ray. He has been shot. He tells Drew that the Dragons have taken his two children and Sydney. Before Drew can escape an attempt to rescue them, the FBI nabs him.
With the help of Wallace, Drew escapes the FBI. He gets into the Dragons' territory and sees a warehouse where activity is centered. Light and dark invaders are battling each other everywhere. Drew battles his way into the interior of the warehouse. He shoots, but does not kill, six Dragons. He eventually reaches Sydney and the kids, only to learn that the leader of the Dragons is using them as human shields.
Drew is forced to lay down his guns when the leader threatens to cut Sydney's throat. The situation appears hopeless, and Drew realizes he will have to give his life to save three. Drew sees Sydney bow her head, and the same blue aura he had seen around her at Drayle flows around her now. Her prayers ward off the dark invaders, and suddenly more than 20 light invaders arrive, and a major battle ensues. Sydney and the two children escape under the protection of a light invader.
When the battle subsides, everyone is gone but Drew and Wallace. As before, Wallace breaks out of his realm and into the world of humans to warn Drew that he is in serious danger. Wallace tells Drew his real name is Validus. Just as he returns to his realm, the FBI show up and arrest Drew.
The book ends with a conversation between Validus and another light invader named Tren. Neither is sure why, but the unbelieving Drew is at the center of a spiritual battle.