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.