Urkel discovers he's able to isolate and then duplicate complex molecules. In other words, he can "clone stuff" - which means double trouble for the Winslows.
Laura and Urkel's prom dates both cancel at the last minute, leaving them to go with each other. Meanwhile, Harriette's obnoxious former boss Mr. Neidermeyer becomes the Winslows' next-door neighbor.
Eddie and Waldo fall victim to a scam when they saunter into a bar expecting to meet members of the Chicago Bulls; Urkel's super glue provides Laura with a super-facial.
Waldo takes tap dancing lessons to improve his agility, and hopefully his basketball game, too. Elsewhere, getting accepted to Harvard means the world to Laura, until she learns her parents can't pay the tuition.
Urkel's powerful love potion prompts a sudden devotion from Laura; airline nightmares plague Carl and Harriette on their way to Nassau for a second honeymoon.
Urkel joins Big Brothers, and learns his street-wise little brother is illiterate. Meanwhile, Carl finds a secret savings account passbook belonging to Harriette.
Eddie takes ballet to improve his basketball skills, but gets a surprise partner to perform Swan Lake with. Meanwhile, Harriette has trouble coming to grips with getting older.
Eddie learns his drinking is alienating both his family and his friends. Meanwhile, Steve looks to earn money by playing jazz as his alter ego, Stefan.
Teamwork and the transformation chamber give Carl and Urkel an advantage in fighting off gang members looking to ransack the police warehouse. Meanwhile, Harriette's upset when Laura gets a nose ring without telling her.
Carl, Urkel, and Eddie head to Porto Santo to free the arrested Waldo. Meanwhile, Laura is reluctant to go on a date with a boy she has never met, but her mother recommends.
Carl becomes enamored with his new car. He also backpedals on his refusal to teach Urkel to ride a bike when it seems that the clumsy kid might wreck his new car. Laura brushes off Maxine's wish to become a hairdresser as foolhardy.
Carl's bah-humbug attitude toward Urkel's rooftop Christmas decorations changes once he learns that winning a decorating contest could bring the Winslows a sackful of holiday cheer. Meanwhile, Harriette is saddened because Laura and Eddie seem to be too busy to participate in family Christmas activities.
Steve is put in charge of building the school's homecoming parade float—then promptly crashes it. Meanwhile, Mother Winslow sustains a series of minor injuries in her strenuous hobbies, including karate and square dancing, making Carl worry she's pushing herself too hard.
Laura and Myra's friendship turns stormy as they compete for the same sales job at Ferguson's; a rainstorm renders Urkel a "human lightning rod" and he refuses to go outside after being struck by lightning three times.
Waldo convinces Steve, Myra, and Laura to appear on a talk show to discuss unfulfilling romances. Everyone is surprised when Myrtle comes on and talks about her unrequited love for Eddie. Meanwhile, Harriette tries to inspire passion in a reluctant Carl.
With Greta forbidden from seeing Eddie, he convinces Steve to pretend to take her on dates so he can see her on the sly. Meanwhile, Mother Winslow gets audited for the IRS.
When Steve becomes substitute teacher, he transforms to Stefan to get some respect and revenge. Meanwhile, Harriette berates Carl for not helping with the housework, so he hires a sexy maid, much to her consternation.
Steve's guilt-stricken over fantasizing about a gorgeous bug collector he met on the Internet. Meanwhile, Harriette regrets making Carl have her boss over for poker night.
While they both get ready to take a shower, Steve and Laura accidentally see each other naked in the bathroom—a traumatic experience for both of them. Meanwhile, Carl's neighbor asks him to hold onto an expensive diamond bracelet because Larry's wife is a snoop, but Harriette finding it complicates matters.
Mischief-maker Urkel and his troublesome transformation chamber move in with the Winslows and he wreaks household havoc by shrinking both himself and Carl in an experiment gone awry.