A computer chip from the U.S. Department of Defense has gone missing, and it contains high-level secrets. International criminals have also driven up its price to an astronomical figure. In order to complete the transaction, the criminals hid it in a toy remote control car and successfully passed the airport security check. However, on the way, it was accidentally swapped by an old lady, and eventually the remote control car with the high-level secret chip was delivered to the hands of 8-year-old boy Alex (Alex D. Linz). In order to retrieve the chip, professionally trained criminals sneaked into the community where Alex lived. One night, Alex was left alone at home because of chickenpox, which gave the criminals a great opportunity. However... Alex was not the 8-year-old boy they imagined. He had unexpected "weapons" and finally defeated the criminals with wisdom. Since the protagonist Macaulay Culkin of the previous two films had grown up when the third film started, the third film used the new protagonist Alex D. Linz.