Plot
John Brown lives in the city of Riverton with his 12-year-old niece, Penny Brown, and her pet beagle, Brain. Dreaming of becoming a police officer, John works as a security guard for the Bradford robotics laboratory. Artemus Bradford and his daughter, Brenda, are designing a lifelike robotic foot as part of the Gadget Program, designed to add android officers to the Riverton Police Department. Sanford Scolex, a malicious tycoon, uses a robotic tank to break into the Bradford laboratory and steal the foot to build an army of androids from its technology, assassinating Artemus in the process. John chases after Scolex's limousine in his hatchback, but John's car gets flipped over due to an oil slick from Scolex's limo, leading both vehicles to crash into a Yahoo billboard. John is blown up in his capsized car by a dynamite stick disguised as a cigar and left for dead, but a bowling ball launched by the explosive blast from the destroyed car lands in the limo and crushes Scolex's left hand; Scolex receives a mechanical claw from his associate, Kramer, taking on the alias "Dr. Claw".
Brenda decides to make John, whose body is now mangled from the explosion, the first test subject for the Gadget Program. She builds an array of gadgets into his body and gives him the alias "Inspector Gadget", inserting a control chip as his power supply. Brenda and a local guru give John an orientation on using his new gadgets, which goes awry when the guru is hospitalized by a pinch to the testicles inadvertently caused by John, causing the guru's voice pitch to rise. He is helped by the Gadgetmobile, a robotic car with a chatty AI. Despite struggling with his new gadgets, John stops two criminals trying to rob a car after stealing a cat.
At a charity ball, Scolex approaches Brenda, having known her at Harvard, inviting her to work for him in her own laboratory. Brenda accepts, unaware that Scolex plans to steal her technological ideas and designs. Unimpressed with John, Riverton Police Chief Frank Quimby assigns him to menial assignments rather than investigate Artemus' murder. Upset at not being taken seriously, John begins investigating Artemus' murder on his own and finds a piece of scrap metal, which he later connects to Scolex with Penny's help.
Scolex uses Brenda's research to build his own android, "Robo-Gadget", sending him out on a rampage across Riverton to frame John, who infiltrates Scolex's lab to recover the foot but is caught and deactivated when Scolex breaks his chip. Scolex's minion, Sykes, dumps John in a junkyard and is then tasked to dispose of the foot. Brenda encounters her own robotic doppelgänger, Robo-Brenda, who confirms that Scolex stole the foot and murdered her father. Brenda, Penny, Brain, and the Gadgetmobile track John to a junkyard, where a kiss from Brenda awakens him, proving John's human willpower can control his new body without the chip.
After dropping Penny and Brain off at home for their safety, John and Brenda chase Scolex and Robo-Gadget's limo. John and Robo-Gadget fall off the roof and duel on a bridge until John removes the latter's head, tossing it into the river, though Robo-Gadget's body strips John's pants off and runs away. Brenda crashes the Gadgetmobile into Scolex's limo but is taken prisoner. Scolex tries to escape in a helicopter with her, but John appears using his helicopter hat to intercept. Scolex destroys it, and John is stuck hanging from the landing skis. John deconstructs a pen in his finger, whilst remembering the "visualizing [his] goal" advice from the guru, and launches the metal ink chamber, sending it bouncing around until it hits a button on Scolex's claw, causing it to clamp shut and break the joystick of the helicopter. Brenda leaps out of the spinning helicopter onto John's back, and they fall down the side of Scolex's skyscraper, using a parasol to land safely. Scolex parachutes down but lands in the Gadgetmobile and is captured by it. The police arrive to arrest John for Robo-Gadget's rampage, but Penny appears with a repentant and reformed Sykes, who confesses his boss' crimes to the police. Saluted and acknowledged by Quimby as an actual member of the police force, John departs with Brenda and Penny while Scolex vows revenge as he is taken away by the cops. The film ends with John and Brenda beginning a relationship, and Gadgetmobile driving after a red car.
