When Harry and George hold a fraternity reunion, Dennis mistakes two escaped convicts for ""frat brothers"". He invites them to join his fraternity, and the practical jokes that follow wind up making the pair wish they had never left jail!

Dennis goes into hospital, frightened by ""mis-informed"" medical facts his friends have given. However, when Mr.Wilson accidently winds up as his roommate, he forgets about his own fears, and sets out to ""protect"" his friend. In the end, Mr.Wilson is so distraught and beleagured by Dennis ""care"", that he begs to be put in the isolation of the intensive care unit! Seeing how ""brave"" Mr.Wilson is, Dennis finally musters the courage to let them do his ""tonsil-neck'tamy"" after all.

Dennis decides he's too big for baby-siters and tells Joey it's time they ""became men"". However, duplicating the exact things Mr.Wilson was supposed to have done as a young man, he soon has Margaret on his case, trying to prove a point for all womanhood. Then, when the kids accidentally wind up on a ""camp out"" with Henry and George, the differences escalate into a ""battle of the sexes"" to see who can survive the woodsy ordeal. Hint: Don't put your money on Mr.Wilson.

Dennis wages an all-out commando strike on the neighbourhood bully. But he inadvertently ""captures"" a toothache-ridden Mr.Wilson instead, and the two are stuck together on a wild odyssey to the dentist's office, filled with ""pains, trains and automobiles"". During their trek, Dennis learns a valuble lesson about the true nature of bullies...and manages to sneak in a little impromptu dentistry of his own!

Dennis's dog is getting into just as much trouble as he is, lately. But Mr. Wilson soon finds out that it's Dennis who is encouraging the dog to get into trouble.

Dennis gets to go hunting with Mr. Wilson. But Mr. Wilson gets fed up because Dennis keeps scaring away all the animals.

Dennis turns the backyard into a construction zone.

Dennis tries to rig a horse race.

Dennis gets aboard a Navy vessel.

Dennis pretends to be Yankee Doodle.

Dennis tries to help his mother for a day, but keeps getting into mischief.

Dennis gets a wish granted for him.

Dennis is mistaken for a brain child.