Harley is an engineering whiz who uses her inventions to navigate life as the middle child in a large family of seven kids.
Harley rallies her siblings and parents to take a trip to Florida to celebrate Christmas with their abuela, but in true Diaz fashion, things go awry. One rerouted flight, an unintended pit stop and a damaged rockstar tour bus later, the Diazes find themselves stranded in a small town without phones, credit cards or money, where they must compete with the town residents in an “Iron Elf” competition to get their bus repaired and make it to Abuela’s in time for Christmas.
When Rachel apparently misses out on an incredible educational opportunity, her sisters are suspicious of how well she takes the news. Meanwhile, Ethan cashes in on his experience of living with four sisters by landing a job.
As the Diazes cope with their new family dynamics, Ethan reluctantly asks his sisters for advice on girls.
As Harley tries to raise money, by running a day camp for the neighborhood kids, in the Diaz backyard, she finds herself distracted by the new neighbor, Ellie's irritating cousin, Aiden.
Harley and Suzy come up with a new way to get along with their neighbors.
Georgie enlists Harley's help to break up with Wyatt.
Harley's latest invention causes havoc in science class.
When the Bait N' Bite is robbed, the Diaz children use their resources to track down the culprit.
Under Abuela's watch for the weekend, the Diaz kids are committed to making her visit disaster-free, that is, until Harley learns that Ethan spilled her deepest secret.
The Diaz family delivers a luxury yacht, living it up until they dock at the port next to the dreaded Pillman family.
When Georgie fails to make the basketball team, Harley helps her cultivate a new passion instead.
Harley goes all out to convince popular neighborhood blogger, Shane Coleman, to feature Ethan's latest film project about Zombies.
Harley learns that her opportunity to meet one of her scientific heroes depends upon her ability to rein in Daphne. Meanwhile, Ethan faces some hard decisions in forming a band for the Marshport Seafood Festival.
Harley build an escape room in an effort to bond with her siblings.
As the Diazes visit Boston, Harley and the twins go to a wrestling event, while Suzy and Georgie scheme to get Rachel's name on TV.
After scheming and plotting to uncover the perfect gift for a certain someone, Harley is dismayed that the recipient is less than enthusiastic upon receiving the result.
When the family car rolls into the garage and causes severe damage, Tom and Suzy look for a culprit; Ethan and Harley don't have alibis, so they head to Diaz Court.
Harley discovers that the confusing circumstances surrounding the time she was born literally cost her dad the vehicle of his dreams, now more than fifteen years later, she attempts to rectify the situation on his birthday.
Ellie volunteers to be the videographer at Harley's upcoming quinceanera, except she does not have a good track record.
It's quince day! Harley enlists the help of the Littles to tackle what's left of her Buck-Kid List before she becomes an official adult.