Wayne Szalinzki, a wacky, absent-minded inventor, is back again but only this time he decides to use his infamous shrinking machine just one more time. His wife, Diane, asks him to get rid of the Tiki Man, a large tiki sculpture. He refuses to get rid of it so he decides to restart the machine and reduces it to pocket-size. However, the machine is accidentally activated and Wayne ends up shrinking himself and his brother, Gordon. Meanwhile, when Gordon's wife, Patti, and Diane were going on a vacation they come back when Patti suddenly realizes she forgot Mitch's medicine for his potassium deficiency. When they're about to leave, they decide to sneak into the attic and surprise their husbands, but the machine is activated once again, and they're shrunk as well. So the adults must be very brave of disgusting household insects the size of dinosaurs and more in their biggest adventure to get their children's attention.