Axl returns home from his summer trip to Europe, sporting a man-bun and embracing a new, chill European outlook on life. Mike just wants him to clean up and look for a job, but Frankie thinks Axl will do this on his own and asks Mike to give him a little breathing room. Meanwhile, because Sue worked the entire summer at Spudsy’s and missed out on having any fun, she decides to cram in a whole summer of fun in two days before going back to college; Brick makes the decision to break up with Cindy because he doesn’t want to be tied down in a relationship when he’s about to embark on the revelry of his “big sophomore year”; and Frankie desperately tries to come up with an item for a time capsule that’s being buried under the Orson cow that will make the town remember the Hecks when it’s opened in 100 years.

After Frankie gives neighbor Nancy Donahue an old scarf that is just sitting around gathering dust, Nancy returns the favor by baking her a delicious apple pie. Believing she’s stumbled upon a way to get free and tasty meals, Frankie makes it her mission to find miscellaneous items around the house to give to her in exchange for some culinary delights. Meanwhile, Sue and Lexie prepare to move back into their college apartment but find that it’s been sublet to a man who refuses to leave; and Axl’s new job as the school bus driver gives him a chance to see how Brick’s high school sophomore year is treating him, and he discovers that Mike has refused to speak to Brick’s class on Career Exploration Day.

Frankie is worried about meeting Lexie's rich parents. Brick discovers that he can't get arrested when he participates in the school's Sophomore Slammer fundraiser.

Frankie discovers that a woman had died in the bathtub of the Heck house close to 50 years ago.

Axl tries to invent a new beverage; Mike asks Sue to put together a romantic evening for his and Frankie's 25th wedding anniversary; Sue declares she won't be the person who does everything expected of her without complaint.

Frankie's mom stays with her after becoming ill; Sue suggests to Sean that they should set each other up on dates; Axl and Brick ponder what Mike actually does at the quarry.

The Hecks take a hectic road trip to Frankie's sister's house for Thanksgiving; the kids must decide which one of them will lose their job at Spudsy's.

Frankie remembers she has to come up with something to place in the time capsule; Bill Norwood informs Mike that he and Paula are separating; Brick tries to win Cindy back; Axl volunteers Sue to be his personal assistant.

Frankie and Sue are devastated when Axl informs them that he's not going to church; Mike goes to war with the Glossner kids after they keep defacing his giant inflatable snowman; Brick attempts to wrap his first present.

Sue admits to Frankie that she kissed Sean Donahue at the Christmas party; Mike forces Axl and Brick to take a drive with him and Mike's dad.

Axl starts to bond more with Mike now that he has a real job; Frankie feels ignored; Brad pleads with Sue to introduce him to Aidan's handsome friend.

Frankie decides that she needs to find something new that she's passionate about—life's third act—and Reverend TimTom offers the perfect solution. Meanwhile, tired of hearing Sue and Brick argue because of the giant hole between their bedroom walls, Mike orders them to fix it; and after Axl refuses to let rich girlfriend Lexie pay for some extravagant outings, Lexie finds a way to fool him into thinking he's becoming lucky when money and other items suddenly make their way into his hands.

Mike's wayward brother, Rusty, comes to town and presents Sue with an extravagant gift, which Mike thinks is stolen goods. Meanwhile, with Sue now older and living the college life, Mike feels like he's not as close to her as he used to be and tries to figure out a way to reconnect; Axl blows the money from his first paycheck on a big screen TV and blames his spending spree on years of learning from Frankie's lack of financial wisdom; and Brick is stumped, but delighted to discover mysterious, unmarked gifts being left at the front door of the house.

Things don't go as smoothly as planned for the Hecks when Frankie helps Sue celebrate her 21st birthday by taking her to a bar close to the college, Mike begrudgingly accompanies Brick to a "Planet Nowhere" convention, and Axl and Hutch head to Ohio in the Winnebago to attend and make a toast at ex-college roomie Kenny's wedding.

While Frankie feels the need to have a good cry after having a bad week, Mike shares the good news that, after 25 years as manager at the local quarry, he is being offered the job of regional manager but feels uncomfortable saying goodbye to his co-workers. Meanwhile, Brick suspects that he's being treated unfairly by his health teacher because of how horribly Axl treated her back when he was a student.

It's the Orson showdown of the century when the Hecks - along with the Donahues and Bill Norwood - wage a war against the Glossners after they steal Sue's car.

Dr. Fulton tells Frankie and Mike that Brick and Cindy have been making out all over the school. Mike tries to teach Brick proper dating etiquette; Sue attempts to give Sean the snow globe, and tell him how much she likes him; Frankie finds a box of unfinished thank you letters, she orders Axl to finish them, and mail them all out.

Frankie is surprised but relieved when Dr. Goodwin agrees to buy all of the peanut brittle that Brick needs to sell for school. But the good doctor displays a bit of Mr. Hyde behavior when Frankie doesn't deliver the product in an expeditious manner. Meanwhile, Axl is getting sick and tired of having Mike tell him how to run his life; and things go off the rails when Axl attempts to trade in the Winnebago and buy a car. Sue is more determined than ever to win a very prestigious and competitive hotel scholarship; and Frankie swears that she's seeing something mysterious flying through the house.

Frankie has to force Brick into asking Cindy to the high school prom but worries that his quirkiness could spoil the happy event; Lexie talks a clueless Axl into giving Sue a belated 21st birthday present; and Mike becomes frustrated over how to get used to a new TV remote.

In an attempt to get Frankie the best Mother's Day gift ever, Sue and Brick enter a trivia contest where they could win a trip for two to London for the upcoming royal wedding; and Axl is offered a job interview that could change his life.

Frankie makes it her mission to sway Axl from taking the job in Denver; Sue is depressed over Sean leaving for Ghana; Brick buys a huge amount of lawn chairs to replace the one he's been using for nine years.

After nine hilarious and heartfelt seasons, a Heck leaves the nest as the family takes a road trip to Denver, where Axl will start his new job – and new life away from home.

The series concludes as the family escorts Axl to Colorado. Meanwhile the long affair of the snow globe and its relation to Sean and Sue's relationship comes to a head.