Dennis successfully eludes a babysitter (whom he has never met) and sneaks out of the house and goes to a cowboy movie that his parents also go to while Joey, pretending to be Dennis, is left with the babysitter. Madge Blake appears as Mrs. Porter the babysitter.

Dennis and Tommy fix a fallen street signpost but fail to notice they've put it up with the street names facing in the wrong direction. Because of the mix up, Mr. Wilson gets a pool dug in his yard instead of it being re-seeded. Suddenly, everyone in the neighborhood wants to be Mr. Wilson's friend.

Henry and Mr. Wilson have a fishing trip planned and are trying to keep Dennis from finding out. Dennis however knows something is up when he sees a package delivered to the house that has fishing stuff in it and so it turns out to be a long night for Dennis as he won't rest until he finds out what's in the package. Eventually he figures it out and so Henry and Mr. Wilson end up taking Dennis along after all.

Dennis tries to fix up his Grandpa Perkins (James Bell) with Miss Cathcart and other ladies in the neighborhood. Miss Cathcart takes an interest in him, sings for him, and pretty much makes him miserable. Robert B. Williams appears as Mr. Dorfman the Mailman.

Mr. Wilson helps an old neighbor sell his house. He tries to talk a retired couple with no children into moving in next door, which almost works until Dennis and his friends come bursting into Mr. Wilson's house and the couple see how loud things will be. So, what happens is the window repair man is moving in next door, and he has 4 kids, which is not what Mr. Wilson wanted at all.

Mr. Wilson returns from a camping trip, inspiring Dennis and Tommy to camp out in the backyard. That night, Mr. Wilson mistakenly thinks the circus train has crashed and the animals have escaped, but the noises are only the Mitchells' neighbors, the Meltons (Dave Willock & Jenna McMahon), playing a sound-effects record for Henry and Alice.

Dennis thinks his father is broke, so he sells bottles in an attempt to make some extra money while informing the neighborhood of the Mitchells' dire straits.

Dennis hopes to meet Whip Crawford, his cowboy idol, after Mrs. Webster (Isabel Randolph) tells Dennis that Whip will be in the community pageant. Whip doesn't want to be in the play because he claims his feet hurt, so he tries to dodge Mrs. Webster and everyone else. Dennis, who doesn't give up, does everything he can to get Whip Crawford in the play including going to his hotel room and talking to Whip himself which in the end works.

Dennis has a tree house that hangs over Mr. Wilson's back yard. Mr. Wilson is not thrilled about it because he thinks that Dennis up in the tree house will scare all the birds away. Mr. Wilson attempts to teach Dennis about bird watching. Dennis takes care of a sick bird, which proves to be the first of its species ever found in their region, prompting a visit by an excited bird club official, Mr. Pomeroy (Maurice Manson).
Note: This is the first of only two appearances in the series of Tommy's father, Mr. Anderson, although he is mentioned in many episodes spanning the show's entire run. Mr. Anderson, who is played by Lee Millar, also appeared in the third-season episode, "Dennis and the Pee Wee League."

Mr. Wilson pays $250.00 for a rare gold coin from a con artist that turns out to be a fake coin. Mrs. Wilson, without realizing what it is, lets Dennis take it to use in a wishing well, which was the town fountain. Mr. Wilson gets arrested for wading in the fountain looking for his coin. Mr. Wilson wishes that Dennis would go on vacation for a week and his wish comes true in the end when he learns that Dennis is going to his Grandpa's for a week. Notes: While at the police station, Dennis mentions on his last visit he was given ice cream. He was referring to an early episode that already had been made, but was not aired until later the first season, called "Dennis Runs Away."

The Mitchells are having a party to entertain one of Henry's clients, Mr. Purdy (Grandon Rhodes), but people are having trouble finding the house. Dennis finds an open house sign and puts it in the front yard and soon the house is over run with people who think that the house is for sale.

Mr. Wilson is plagued by a duck that Dennis adopted when its original owner moved away. At first Dennis hides the duck from his parents, but when Mr. Wilson complains about the damage caused to his garden and himself, Dennis reluctantly admits to having the duck. His father helps Dennis build an enclosure for the duck, but Mr. Wilson continues to have problems with Dennis' new pet -- and begins to scheme how to get rid of it even if Dennis and his parents won't.

Dennis and a bunch of other town boys are collecting papers for a charity and the prize for the boy who collects the most papers is a Silver dollar. When Mr. Wilson gets word of that, he looks up the value of the Silver dollar and finds it's worth $600. He is determined to make sure that Dennis wins the prize so that he can get the silver dollar.

Dennis needs to earn some money to buy some pet mice. Dennis goes to Mr. Wilson's house to see if there's any job he might have for him to do. While there, one of the mice gets out of the cage. Dennis catches the mouse, but messes up George's chess board. Meanwhile, Henry hires a sitter for Dennis for that evening. George tells Henry that he's having dinner with chess champion Monsieur Boucher and his wife, Madame Boucher (Hanna Landy). The problem is that they brought their son Michel with. George arranged for a babysitter for Michel. Henry suggests Michel stay with Dennis. Henry and Mr. Wilson mistakenly both cancel their respective sitters. Michel is dropped off at the Mitchell house. Another misunderstanding causes the boys to be left alone. Dennis decides to be the babysitter. The Mitchell's and their guest run into George and the Bouchers at the same restaurant. There they discover that both sitters were cancelled. They race back to the house only to find everything is OK. Dennis gets paid the money he needs for the mice.

Ed and Catherine Driscoll (Arthur Hanson & June Dayton) are new neighbors, but problems arise as their phone is on a shared line with the Mitchells. Henry gets angry at Mr. Driscoll for monopolizing the line, not realizing that Dennis and his friends actually were the ones using it, and furthermore that Mr. Driscoll is a valued client of Henry's company.

Dennis has nobody to play with after Joey goes home. With everyone else busy, and since nobody can drive him, he decides to walk to his grandfather's house but is stopped by the police. At the police station, he refuses to tell his name, is given ice cream, and causes further havoc including putting cement in Mr. Wilson's bowling ball and accidentally handcuffing an officer.

Alice will be out of town for a while to take care of her injured father. Dennis gets his mother some earrings for a going-away present. Misunderstanding something Mr. Wilson says, Dennis hides his present on Mr. Wilson's closet shelf. Martha finds the present and thinks it's for her, as it's a special day. Not knowing what special day it is, George can't bring himself to tell Martha the gift is not for her. George tells Dennis what happened and says they'll get his mother other earrings. Back at Mr. Finch's store, Dennis can't find earrings that he likes as much as the ones he bought before. Dennis says he'll just have to get the earrings back from Mrs. Wilson. Mr. Finch then railroads George into buying an expensive bottle of perfume for Dennis. Dennis comes home with the present just as Henry's mother shows up to fill in for Alice. The Wilson's come by the say goodbye to Alice. Dennis explains to Henry about the mix up with the earrings and Martha overhears it. Martha confesses that when she saw the gift, she thought it was for a special occasion that she forgot about. Dennis almost causes another mix-up, but everything works out.

Mr. Wilson is mixing up a new plant food. Dennis is arguing with Margaret about what to name one of his frogs. Tommy wonders if they'll ever like girls when they're older. Dennis and Tommy watch as George feeds one of his plants the new food. Dennis accidentally steps on that plant while chasing a frog. The boys get an identical, but much larger, plant from Tommy's yard. They replace it in the flower bed without Mr. Wilson knowing. When Mr. Wilson sees the plant, he is convinced that the new miracle plant food he invented is the cause of the growth. He calls Mrs. Schooner from the garden club and wants some members to come over and see it. Tommy tells Dennis that his mother wants her plant back. Tommy then puts George's original plant back in its place. The garden club come by and see the smaller plant and think George was lying to them. But, they'll give him another chance and let George put more food on it. Dennis goes to Mr. Merrivale (Will Wright) and tries to buy another plant with Dennis's frogs. The boys do make a deal with Mr. Merrivale and get the plant. The garden club come back later, see the larger plant and congratulate George. Dennis comes by and tells the club what really happened. The club members just laugh the whole thing off. Jonathan Hole as Mr. Trumble.

Dennis learns that Mr. Wilson would've liked to have had his name in the newspaper. Dennis and Tommy start their own newspaper, "The Mr. Wilson News", in which they write about Mr. Wilson's daily activities. They overhear George playfully telling Martha that he'd give $20 for a raccoon coat like the one he had in college. The boys put that in their paper and then tell Mr. Krinkie (Charles Seel), who prints the information in the local newspaper. George and Martha are going away for the day. A man (Jess Kirkpatrick) comes by the Wilson house with a racoon coat and sees Dennis. Dennis gets into the house and lets the man in to leave his name and number. In no time, the Wilson household is overflowing with raccoon coats from sellers from all over town. When George comes home, he can't believe what he's seeing. He tries calling all the people, but no one will come for their coats. Chuck Long (Jimmy Hawkins), a young man, comes by and would like to buy one of the coats. Soon, George is able to unload all the coats and the young men will pay the original owners. The local TV news does a story about all the high school boys with the coats and George gets to be on TV.

George and Henry purchase a house as an income property from real estate agent Mr. Bowers (Harvey Korman). After the men leave, Bowers calls his mother, Mrs. Bowers (Kitty Kelly), and tells her he sold the broken down old house of hers. Sgt. Mooney (George Cisar) tells George and Henry that a fast talking real estate agent sold a haunted house to a couple of unsuspecting guys. George, Henry and Mooney speak with Bowers and his mother about getting their money back. The sale was done legally and there's nothing George and Henry can do. They go to the house and the Tramp (Harold Gould) that's been living there hides in the basement. Dennis and Tommy come by and say they'll look for the ghost. Pretending to be a ghost, the Tramp talks to the boys through the duct-work. Dennis tells Henry about the ghost. Henry and George decide to sleep inside to prove that it isn't haunted. That night it starts to storm. George and Henry hear something outside. Sgt. Mooney comes in the house and the men throw a sheet over him. The noise wakes the Tramp in the basement and he makes eerie noises through the duct-work. Dennis and two friends arrive at the house covered in sheets and look through the basement window. This frightens the Tramp and he runs upstairs and is discovered by George, Henry and Mooney. The Tramp says he'll be leaving for Florida.

Dennis' school is putting on a play about all nations. Each student has to ask someone to represent a different nationality to be in the play. Dennis, who's part Scottish and many other countries wishes to represent Scotland, but his parents decline to participate. So Dennis asks Mr. Wilson, who has Scottish ancestors, but he is not interested, either. Dennis then asks Mr. MacTavish (Tudor Owen), who accepts. Once Mr. Wilson finds out there are prizes involved, he wants to be in it. Dennis asks Mr. Krinkie to decide after they each put on a performance. A letter arrives stating that Mr. Wilson is actually Irish. Dennis suggests Mr. Wilson can represent Ireland instead, but the mailman is already doing so!

It's Mr. Wilson's birthday and he decides to leave Dennis a gold watch in his will. Soon after, Mr. Wilson begins to feel old and is convinced that he has a short time to live. Dennis in return, goes to Mr. Phillips (Ray Teal), an attorney, to have a will drawn up so he can leave his favorite things to Mr. Wilson. Dennis gives Mr. Wilson a copy of his will as a birthday gift. He is so touched that he gives Dennis the watch.

George is expecting a visit from his Uncle Ned (Edward Everett Horton), a rocker-chair addict. When Ned arrives, he is active, fit, and energetic. Ned forces George and Henry into a fitness program. As the two struggle to keep up, they plot a way to end the exercises.

Mr. Wilson plans to have a quiet evening at home with his coin collection. His plans change when Henry needs a sitter for Dennis. Mr. Wilson is talked into being a sitter for Dennis, Margaret, and Seymour. Seymour finds one of Mr. Wilson's rare dimes, goes down the street and buys a candy bar from a vending machine. John Astin appears as the policeman who arrests Wilson trying to retrieve his valuable coin from the vending machine.

An Indian fire-starting demonstration is to take place for Dennis' Junior Pathfinders club, but the person who is to do perform the demonstration hurts his back. Mr. Wilson, trying to get into the Pioneer Club, is volunteered to be the replacement Indian chief and has to start a fire by rubbing together two sticks. Fearing he might not be able to start the fire, Mr. Wilson has his cousin Fillmore, a chemist, put something on the sticks to insure a fire. This leads to an unexpected result.

Mr. Wilson installs his own burglar alarm after a series of burglaries in the neighborhood. Dennis and Mr. Wilson think the new neighbor is the stocking bandit. While trying to prove the neighbor is the bandit, Mr. Wilson gets stuck in their basement window.

Mr. Quigley, though lacking experience, is named coach of the town's pee-wee baseball team, hoping it will help advertise his store. The mayor agrees to give the team new uniforms if Quigley can get Sandy Koufax and the Dodgers to play an exhibition game in town. Quigley is nervous around Sandy and the kids begin to question if he can really coach their team. That is until Quigley hits a home run off Sandy.

George's Uncle Ned visits while George is out of town. He decides to plant flowers to win a flower contest in the summer, but he hurts his back. Dennis gets an older friend named Jerry to help Uncle Ned, but Jerry keeps thinking about his ex-girlfriend Helen (Cheryl Holdridge) and gets nothing done. Helen makes up with Jerry and helps with the bulbs, but she plants them all upside down.

George Wilson's brother, John, comes to stay with Martha while George is out of town. John is a writer, but has trouble working without his old seat cushion. Dennis makes it his goal to make a cushion for John. Dennis also helps John get out of speaking at a lecture. Elvia Allman appears as Isabel Tolliver, a woman who wants John to lecture at her Literary Club.

After being picked on by Gifford Kelly (Mickey Sholdar), the school bully, Alice makes Dennis promise not to fight. As a result, the bully gives Dennis a black eye. Henry gives Dennis the go-ahead to fight back next time. John Wilson teaches Dennis how to fight and Dennis gives Gifford a black eye. The man that Henry and John hope to rent their investment house to turns out to be Mr. Kelly (Richard Reeves), the bully's father, creating an awkward situation.

Dennis wants to join an older boys' club run by a boy named Walter Hooper (Billy Hughes), but in order to do so, he has to go through an initiation. Walter has Dennis find a goat, a derby hat and a bugle. Dennis stores these things in Mr. Wilson's garage. John sees these things and begins to question his sanity, because as fast as Dennis and others put this stuff in the garage, Walter takes them out. John Wilson is planning a round of golf with Dr. Fred Ferguson, but he tells the doctor what he sees. Dr. Ferguson believes John is hallucinating until he sees the goat himself.

Mr. Brady (Laurence Haddon) and Tiny Hawkins (Russ McCubbin), an employee at his store, challenge Henry and John Wilson to compete against them in the sporting events at an upcoming community picnic. The Brady team and the Wilson team are tied, with the egg toss being the winning event. When Henry gets his hand stuck in a pickle jar, Dennis must fill in. Dennis and John win, but because Dennis inadvertently used a hard boiled egg. They must now tell Brady.

John Wilson is writing a magazine article about voodoo. Dennis gets the wrong idea and tells the whole neighborhood that John is a witch doctor. Some strange occurrences and odd accidents convince his new neighbors that he really is a witch doctor and is out to hex them. John hosts a party to meet all his neighbors, but everyone is afraid to show up. Dennis makes sure that things work out.

Dennis becomes a fast friend of Sen Yuen (Cherylene Lee), a girl from British Hong Kong, who is staying with the Wilsons. Margaret becomes jealous of Dennis' attention to her. After Sen Yuen kisses Dennis, Mr. Wilson tells Dennis that Chinese girls often marry very young. When Mr. Yuen comes by, Dennis tells everyone he can't marry Sen Yuen as he is already engaged to Margaret.

Dennis overhears and repeats part of a conversation between John and Eloise in which they decide to no longer play cards together. Rumors around the neighborhood begin to fly that the Wilsons are splitting up. Miss Cathcart and Miss Tarbell (Alice Pearce) get a makeover and make a play for Mr. Wilson, each hoping to be his girlfriend. Each woman enlists Dennis to find out more about Mr. Wilson's situation.

Dennis and Mr. Spivey (Leslie Barrett), his school's new principal, get off on the wrong foot after the principal takes a remark about his height the wrong way. He threatens to kick Dennis off the baseball team if he observes any further impudence. Johnny Brady wants Dennis off the team, so he draws an unflattering picture of Mr. Spivey on a paper with Dennis' name on it. This results in Dennis being kicked off the team. With Henry out of town, Mr. Quigley, Mr. Finch and Mr. Wilson each go to see Mr. Spivey pretending to be Dennis' father.

Mr. Wilson hangs out and plays with Dennis and his friends for the day to gather information for a magazine article about the changing behaviors of children. That evening Mr. Wilson throws a weenie roast for the kids. While starting the fire for the grill, Dennis accidentally burns all of John's notes that he took during the day.

Mr. Wilson takes over an advice-to-the-lovelorn newspaper column for a few weeks. He thinks he will have every single woman in town happily married by the time he finishes. However, complications arise when he unwittingly gives advice to two women - Miss Cathcart and Miss Tarbell - who are out to catch the same man, Sgt. Mooney. Stafford Repp appears as Police Chief Doyle.

Note: This episode marks the final appearance in the series of Mary Wickes, who played Esther Cathcart, and the second and final appearance of the fourth season by Alice Pearce as Lucy Tarbell.

Mr. Wilson is named chairman of a saving-stamps campaign for the Junior Astronauts. As chairman, he arranges a contest at Dennis' school in which the student who collects the most stamps wins a trip to Cape Canaveral to meet an astronaut. Dennis and Johnny Brady are leading the contest, but then Dennis comes down with Chicken Pox and can't continue. But, Dennis does get a special message that makes him feel better. Guest appearance by Project Mercury spokesman "Shorty" Powers as himself.

Stretch Nichols, the school basketball team's star player, quits the team after being teased about his height and worn-out clothes one time too many by Johnny Brady and some of the other players. When Mr. Quigley hears that Stretch quit, he bets Mr. Brady that the team will lose. A sympathetic Dennis persuades Mr. Quigley to help by buying Stretch new clothes and giving him an after-school job, so that Stretch will feel better about himself and rejoin the team in time for the big game. Despite sore feet from the new shoes, Stretch leads the team to a victory. And Quigley gladly pays off on his bet. Bob Hastings appears as Coach Gilmore.

Mr. Wilson enters an essay contest that requires the entrants to be parents. He hopes to win a large sum of money. When he wins the contest, he tries to pass off Dennis and his friends as his own children. Mr. Wilson assumes the contest judge (guest star Harvey Korman) is calling at his door, but it proves to be instead an angry motorist whose car the children had damaged. When Mr. Griffin, the contest judge, finally arrives, it turns out the prize is a free pair of shoes for each of the boys.

Property taxes have risen, and Mr. Wilson thinks the reason is that the school is wasting money on nonessential programs and luxuries. So the principal invites Mr. Wilson to spend the day as a regular student. Harold Gould guest stars as Dennis' principal.

Mr. Wilson and Mrs. Elkins are each running for president of the Birdwatchers Society. The first mockingbird of spring has made its nest in Mr. Wilson's backyard, and its chirping keeps him up at night. When Mrs. Elkins finds out that John has removed the mockingbird's nest, she believes she has the upper hand. However, thanks to Dennis, John comes up with some incriminating evidence against her.

In the series finale, Mr. Wilson's Aunt Emma visits and takes an instant liking to Dennis. This causes Mr. Wilson to fear that she will make Dennis her heir instead of him. John becomes more and more worried as Aunt Emma and Dennis spend more and more time together. In the end, Aunt Emma leaves a pirate sword to Dennis and all her money to Eloise.