Arnold and Gerald are cast as a banana and a strawberry in their school play which is written and directed by Helga. Arnold wrecks Eugene's brand new bike.
Helga drops her journal full of love poems about Arnold into a pile of books. Arnold's class goes on a field trip to the aquarium where Arnold waits to see Lockjaw.
Helga has been secretly building a shrine in her closet to Arnold, but only one thing will make the shrine complete: Arnold's hat. Arnold has to retrieve the football from the lair of the legendary Stoop Kid -- a bully who, according to neighborhood legend, pounds anyone who sets foot upon his domain.
Helga tries to hide her disappointment at not being invited to Rhonda's makeover party. She gives herself her own makeover and crashes the party. Arnold gets caught between his loyalty to Grandma and a promise to help his pal Ernie demolish his 500th building when the demolition of an old theater brings Grandma and Ernie into conflict with one another.
Arnold and Gerald are invited to a school dance by Connie and Maria; a pair of 6th grade "older women" who are trying to make their boyfriends jealous. Arnold and Gerald manage to scrape up enough money for cheap seats at the last baseball game of Mickey Kaline - Arnold's idol. Arnold snags a home run ball, but he learns the home run ball would mean even more to somebody else.
A record heatwave strikes the city. Arnold and Gerald look for relief from the soaring temperature, but snap when they learn the ice cream man is price-gouging kids for his product. Arnold wakes to find the city covered in snow and hears that school is closed for the day. He wants to go out and join the rest of the neighborhood, but sees that Grandpa is busy with extra work due to the storm.
Arnold decides to get up the nerve to speak with the girl of his dreams, Ruth McDougal, at the annual cheese festival. Arnold and the gang clean up a vacant lot so that they can have a baseball field, but the neighborhood adults have designs of their own for the newly renovated space.
Arnold's best laid plans for the "ultimate Saturday" go up in smoke when he tries to complete all of his favorite things to do in one afternoon. On a boring summer night Grandpa tries to liven things up by telling a story about haunted Train Number 25 which comes back to earth on the anniversary of its last ride -- the mad engineer wants to take unsuspecting passengers away to the spirit world!
Arnold learns the secrets of the martial arts from Grandma after getting held up for his bus pass. Grandpa takes Arnold and Gerald out to the woods to show them how to camp "the old fashioned way."
The boarders are all suspicious of the mysterious Mr. Smith who lives behind door 16. He has a private bathroom and takes all his meals alone. Oscar Kokoshka moves in with Arnold when his wife, Susie, throws him out of their apartment following another fight. Arnold resolves to get the two back together again after his new "roomie" starts to drive him crazy!
Arnold has trouble with the basketball coach and his favored son until he teaches them both a lesson in Zen and the Art of Free-throw Shooting as well as the real meaning of teamwork. Arnold becomes friend with "cool" Frankie G., but his new friend only succeeds in getting him into trouble.
When a movie lets out later than expected, Arnold and the gang have no choice but to take the subway home. Arnold and the gang set out on a quest to find the hidden treasure of the mysterious "Wheezin' Ed" on Elk Island. They recruit a salty old sea captain to ferry them to the island where they find themselves pitted against a couple of penny counterfeiters hiding out in the island's caves.
Arnold is given the assignment to tutor Torvald, the meanest, toughest kid in Arnold's math class, for the big math test on Friday. Gerald convinces Arnold to allow him to spend the night at Arnold's house. Arnold is apprehensive about introducing his friend to his extended "family"; the sometimes eccentric boarders at his Grandparents' house.
Arnold and Helga are chosen to represent the school in the city wide spelling bee. Arnold has serious plans for the $500 prize money, but Helga has other ideas. / Arnold takes one of his sick pigeons to the mysterious Pigeon Man who miraculously cures the bird. To show his gratitude, Arnold convinces the Pigeon Man to come down off his roof and walk around the old neighborhood.
When Helga's older sister, Olga, comes home from college and gets all of her parents' attention, Helga plots to sabotage her sister's visit by altering her college grades. / Arnold and Gerald save up cereal box tops to get a telescope before the arrival of Salley's Comet.
Arnold's pet pig, Abner, escapes one night while Arnold is sleeping. / When Arnold tries to bring Grandpa's pocket watch home from the repair shop, Arnold accidentally drops it down a hole in the street. He plunges into the darkness to retrieve it and finds himself in a strange subterranean world ruled by the self-proclaimed King of the Sewers who has no intention of giving up his new watch!
Eugene is falsley accused of pulling a fire alarm. Arnold acts as Eugene's advocate before the student jury who all want to wrap up the case quickly before Wrestlemania begins. / When Arnold becomes fascinated with the Book of World Records, he and Gerald set out to set a world record of their own.
Arnold gives an amateur magic show behind the boarding house and, for his big number, makes Helga actually disappear. / When Arnold accidentally beans Harold in a baseball game, the bully vows to "kill" him, and gives him 24 hours to live.
When Arnold draws Mr. Hyunh's name in the boarding house's Secret Santa, he decides to make it the most special Christmas ever for the lonely boarder and tries to reunite Mr. Hyunh with his long-lost daughter.
It's Valentine's Day and Arnold must navigate his way between two dinner dates at French restaurants directly across the street from each other.