The NSA-funded QT (Quantum Tech) Corporation has slated a project to develop Hypertime, a technology which allows the user's molecules to speed up to the point where the world appears to be standing still. After realizing that such technology, contained within a wristwatch frame, could also be used against the USA, the NSA orders the project stopped. However, the research is farther along than the NSA expected and Henry Gates, the head of QT, plans on using the technology to usurp the leader of the NSA and dominate the world. He uses the prototype to stretch the weekend in order to give the brilliant lead scientist, Earl Dopler, time to fix the remaining glitch in the technology after his henchmen Richard and Jay prevent Earl's incognito departure at the airport. However, the disadvantage of Earl being in Hypertime for too long was him aging rapidly in real time, as his molecular age continued at the same rate despite time slowing down.
However, initially unknown to Gates, the lead scientist had sent a prototype to a former colleague of his named Dr. Gibbs. His son Zak discovers the watch accidentally and initially uses it for his own purpose, much to Francesca's amusement. Once Gates finds out about the leaked prototype, he attempts to retrieve it. He sends his henchmen after Zak, who break into his house and search for evidence. Upon learning about the ulterior motive of QT Corporation, Zak sets out to warn his father of the danger he could be in.
A chase sequence ensues, with Zak crashing the car into the river and thus damaging the watch. He awakes in hospital with a broken watch, and only by a stroke of luck manages to avoid Jay and Richard again. He then goes in search of somewhere safe to hide in the meantime.
In a bid to retrive the watch, QT Corporation enlists the help of national security agencies and portray Zak and his father as fugitives wanted by the law. Zak goes on the run with his girlfriend, locating the hotel that Dr. Gibbs was staying at in a bid to warn him. However, QT Corporation reaches Zak's father before him and takes him away.
Unable to reach his father, Zak and Francesca wander the streets aimlessly before being forcibly picked up by Earl Dopler, who has escaped from QT Corporation and wants the watch back. The teens take Dopler hostage and force him to do as they request. As Dopler feels that Dr. Gibbs has been kind to him, he agrees reluctantly to helping save Dr. Gibbs.
Dopler helps mend the broken watch as well as creating guns which can take someone out of Hypertime and back into normal time. The guns are loaded with paintballs filled with frozen nitrogen, and the low temperature 'freezes' a hit person back into normal time.
Dopler helps the kids break in but decides not to go as well. They get caught by Henry Gates, Richard, and Jay and are thrown in a cell with Zak's dad. Zak accelerates while in Hypertime and becomes "light" (Einstein's theory is seemingly correct, anything faster than "light", becomes "light"). They then manage to break out as the NSA Agents arrives and defeat Gates' goons. Gates is not defeated and knocks Francesca out of hypertime and prepares to do the same to Zak and his dad. Suddenly he's shot with a paintball by Dopler who returned to help and Dopler shoots Gates until he reverts to normal time, defeating him. Gates and his henchmen are arrested, and the watches are confiscated.
Following the arrest of Gates, Dopler uses the machine he was building to reverse the aging effects of hypertime that happened to him, but it inadvertently changes him back into a teenager. The movie ends with Zak and his family happily together, and with Zak finally getting the car he wanted. As Zak speeds off in his car with his girlfriend, sister and Dopler, it is revealed that he has not returned the watch after all, as he goes into Hypertime to evade a chasing police car.