Hey, Mr. Wilson! It's another Dennis the Menace movie! The day starts out fine, it's Mr. Wilson's birthday and guess who shows up uninvited? Dennis and a few of his bug friends. After getting a cake in the face and falling down the stairs in a wagon, Mr. Wilson wishes Dennis had another old man to bother. His prayers are answered when Dennis' grandfather comes over announcing he's gonna move in! So once again all is fine until Mr. Wilson finds out he's getting old and Grandpa can do everything better than Mr.Wilson. One day at an amusement park, Mr. Wilson meets The Professor and his assistant Sylvester who claim to be specialists in making people younger--for a price. It's a scam but Mr. Wilson is to naive to know. Well the first few attempts at decreasing Mr. Wilson's age fail, thanks to Dennis. Mr. Wilson tries to do things better than Grandpa when he follows them to the swimming pool but he fails. But it's young Dennis who catches the swindlers at their own game when Wilson wants ...