Plot
During their summer vacation with their grandfather Mori, 15-year-old Rocky, 14-year-old Colt, and 9-year-old Tum-Tum take a test in pitch blackness on an obstacle course. They manage to complete the course yet fail to learn how to use their other senses in place of sight. Later that night, Mori overhears Rocky and Colt planning on not returning the subsequent year due to them growing older, leaving Tum-Tum by himself. Mori becomes depressed at this.
Returning home, Tum-Tum also becomes depressed after learning that his favorite TV show, Dave Dragon & the Star Force 5, is going off the air soon from cancellation, and not even his favorite sandwich was made to cheer him up, which confuses his mother, Jessica. The next day, they meet a new neighbor, Amanda, who accidentally crashes her remote-controlled helicopter into their house's window. To recompense, Jessica invites her over for breakfast and attends Tum-Tum's birthday party at Mega Mountain, an amusement park modeled after Six Flags. Once they arrive at Mega Mountain, Rocky goes to spend time with his girlfriend, Jennifer, and her few friends, Veronica, Eric, and Doyle, while Tum-Tum convinces Colt to join him to watch the performance. While the kids are enjoying themselves, a master criminal named Mary Ann "Medusa" Rogers and her henchmen sneaks in and commandeer the park, disabling many rides and shutting the place down, hold the patrons hostage and then infiltrate the park's command center operations as their secret base. Medusa threatens the park's owner, Harry Jacobsons, to pay the $10 million ransom in exchange for the park's guests' safety. Meanwhile, Tum-Tum and Colt want to get an autograph from Dave until they witness and save him from being captured by Medusa's henchmen. Rocky rejoins his brothers and Amanda, fending off the men after spotting them on the surveillance camera monitors. The boys and Amanda realize the park has been compromised and reports Dave about the situation, who the went off by himself to fight them. The boys and Amanda uses the radio and contacts with the emergency service. The police and fire units is sent to investigate the park. However, Medusa and her men spots and ambush the police, which causes the FBI to arrive at the park for backup. In retaliation, Medusa orders her Jamaican sidekick, C.J., to increase the Avalanche ride's speed level. The boys and Amanda rescue the riders by fighting some of the few men with Amanda's special arsenals that she possesses while she overrides the ride control with her laptop.
Knowing that they will interfere with her plans, Medusa sends her three dim-witted nephews, Carl, Buelow, and Zed, to capture them, but they are taken down by the boys, who use the park's carnival game items and a ride with their ninja skills. Meanwhile, Dave sneaks into the command center, but is quickly discovered and captured by Medusa and her henchmen. The SWAT team arrives and attempts to storm the park through the fence, but is counterattacked by the mercenaries with their trap set with electricity. In the meantime, Amanda utilizes the park’s central control systems with her laptop to lock the ride access down with C.J. trying to wrestle the controls from her, but Medusa quickly accesses the Zinger roller coaster's emergency brake that stops the ride on the inversion. Dave tries to attack Medusa, but she subdues him and orders her men to imprison him in the middle of the roller coaster bottom with the several guests.
Recognizing the picture of Rocky and Jennifer on the ride monitors, Medusa's nephews capture and tie her to the bottom of the Zinger roller coaster loop tracks, at which Medusa threatens to crush her if they don't cooperate. Rocky goes off on his own to rescue Jennifer. Medusa sends her second-in-command, Lothar Zogg, out to capture the boys so they don't interfere. Afterwards, Dave, regaining his confidence, fights off the men and liberates the hostages. Rocky arrives to rescue Jennifer, but he gets attacked by Lothar with a Katana. After a fight that leads to both Rocky and Lothar ending up at the top of the roller coaster loop, Rocky knocks Lothar off by throwing a yo-yo around his ankle to make him bounce out of the park and into the hands of the authorities stationed outside the park. Rocky then manages to free Jennifer before Medusa releases the roller coaster that can crush them. Jacobson arrives via helicopter with several bags of money to pay the ransom for Medusa, but Amanda manages to destroy the last bag with her remote-controlled helicopter, causing the money to rain down onto the park.
Amanda is quickly captured by Medusa, who escapes underground with the remainder of the money. When Dave fends off Medusa's ninjas, she knocks him out unconscious. The boys successfully manage to defeat some of Medusa's ninjas until she shoots all the lights out. After Medusa darkens the halls, Medusa's ninjas fight the boys with their night vision goggles. Despite the disadvantage, the boys overcome their weakness in the dark with Mori's advice about using their senses inability. The boys successfully defeat Medusa's ninjas to rescue Amanda, who is handcuffed, next to a bomb that Medusa activates to destroy the park. The boys rescue her, but they cannot disarm the bomb due to the short-circuited power supply. They decides to attach the bomb taped with a few oxygen tanks with Dave's help to knock off the tank's valves and send it off like a torpedo down towards Medusa's ship where she and her remaining men spots it and dive off before the bomb explodes and destroys her ship on impact. Alerted to the explosion, the police arrive and arrest Medusa at the beach shore, who resigns herself to defeat.
Now hailed and commemorated as heroes even reuniting with their parents and grandfather, the boys give the credit to Dave Dragon and hail him as the real hero to the press media. Rocky and Colt assure Mori that they will not be leaving their training. They also extend the offer to Amanda to come and train with them for the following year, and she gladly accepts. The film ends with everyone celebrating Tum-Tum's birthday.
