Twelve-year-old Jesse Rigsby isn’t a big video game player. His best friend, Eric Conrad, loves them. Eric is currently testing an unreleased game called Full Blast created by their friend Charlie’s father, Mr. Gregory. One day, Eric calls Jesse insisting there’s something he has to see. Jesse walks over but can’t find his friend anywhere. He hits a few buttons on Eric’s video game controller and finds himself inside the game.
With the help of a computerized drill sergeant in the game’s tutorial, he learns how to blast the aliens shaped like bats, praying mantises and sand monsters. He finds Eric, who assures him they can’t really die in the game. Eric also says there are easy escape routes when they want to return to the real world.
The boys use jet packs to travel through different levels, each of which mirrors a famous city. Jesse is beginning to enjoy himself when the boys blast an enemy creature at the same time. The game wasn’t built with this scenario in mind. Their action causes an error that initiates a Hindenburg protocol.
The boys realize the game is glitching and they’re trapped inside. As they try to fight their way past the aliens, a man rescues them and drives them through a crocodile-infested swamp on a hover tank. They learn the man is their former classmate, Mark, who went missing a month earlier. Mark looks like a grown man and says he has been trapped in the game for 20 years.
Mark explains the Hindenburg protocol is an action built into the game to repair errors. A character in the game is designed to fix any glitches that occur. Now, because Jesse and Eric created a problem, the Hindenburg character is after *them*. Errors, like Jesse and Eric, are to be sent to the Black Box from which there is no escape.
With Mark’s help, Eric and Jesse battle more aliens and evade the Hindenburg to find themselves back at the beginning of the game. They shoot the drill sergeant, causing him to fall on and destroy the Hindenburg. The boys are zapped back into Eric’s house, but Mark isn’t with them.
The boys visit Mr. Gregory and explain what’s happened with the game he created. They tell him Mark is still trapped inside. Mr. Gregory tries to deny the possibility of what they’re saying, but he looks nervous and pale. Two weeks pass, and no one sees or hears from Mr. Gregory.
Jesse wakes from a bad dream about his time in the game. An action figure of the drill sergeant sitting on his nightstand tells him he needs to go back in and save Mark. Jesse accepts the challenge.
Several pages at the end of the book describe some basic programming commands (“if,” “then” and “else”) and how they function together in a game.