Wayne Szalinzki, a wacky, absent-minded inventor, is back again but only this time he decides to use his infamous shrink machine just one more time. His wife Diane asks him to get rid of the "Tiki Man" a large tiki sculpture. Wayne refuses to get rid of it so he decides to restart the shrink ray and reduces the Tiki Man to pocket-size. However, after Wayne shrinks the Tiki Man the machine is accidentally activated and Wayne ends up shrinking himself and his brother Gordon. Meanwhile, when Gordon's wife Patty and Diane were going on a vacation they went back to the house when Patty suddenly realizes she forgot Mitch's medicine for his potassium deficiency. When they were about to leave, they decide to sneak into the attic and surprise the men, but the shrink ray is activated once again, and the ladies are shrunk as well. So the team must be very brave of disgusting household insects the size of dinosaurs and more in their biggest adventure to get their children's attention.Mischief device, created by Wayne Szalinski, mess up again - this time not the children have shrunk, but the adults themselves.