Gabby Duran's principal assigns her to a challenging task, namely to look after a bunch of kids from outer space who have been living on Earth in the guise of humans.
Gabby is conflicted about keeping a lid on her unconventional task, as she contemplates telling her friend Wesley, who is obsessed with aliens, about it.
Gabby's attempt to get to the bottom of a rumor about her at school threatens to blow the cover of an alien kid.
As Gabby catches feelings for a boy at school, she inadvertently causes him trouble.
As Gabby feels jealous of Susie Dustman, the new babysitter whom Dina hired to take care of Olivia, things get out of hand when she starts competing with her.
With Dia DE la Dina drawing closer, Gabby tries to give her mom a gift that would make her forget last year's unfortunate incident, all the while Principal Swift's mission on Earth is nearly over and he's getting ready to go back home.
As Principal Swift's replacement turns out to be a disaster, Gabby finds out that Swift hasn't left Earth, so she sets out to persuade him to have his job back.
With Christmas approaching, Gabby's dad promises to spend it at Havensburg, however, he fails to show up, so Gabby decides to take action with Swift's help. Meanwhile, Jeremy and Wesley attempt to capture the villainous White Beard.
Gabby is determined to hold Jeremy's birthday party at her house, but soon things take an unexpected turn as surprise guests start showing up.
As Gabby decides to have Sky over for a fun sleepover, Sky's dad warns Gabby of going overboard.
Much to her surprise, Gabby finds out that Wesley has been keeping a journal, in which he wrote about the alien kids he has met with her, upon which the two get called to the principal's office.
After getting a note from an anonymous person who claims to know about Gabby's secret, she and Wesley set out to find the sender, only to receive another note that contains a threat.
Gabby somehow gains great intelligence after Jeremy sneezed on her, whereupon she uses her newfound academic genius to enter a math competition against her nemesis, Susie.
Gabby is excited about the upcoming middle school dance, yet things don't go as planned, as Wesley asks Rhonda, his eccentric friend, to come with them.
When Gabby and Olivia learn that Dina is thinking about moving back to Miami, they try to keep her preoccupied with her job at the news station by enlisting the help of some aliens.
Following an awkward incident, Gabby and Wesley decide to borrow an alien memory-erasing device that hasn't been tested, but their plan doesn't pan out.
Gabby has Swift on her back, as a family for whom she had babysat complained about her, whereupon she sets out to prove to Swift that there's something fishy about them.
As Gabby and Wesley help during the preparation for the party of the Luchachos's 25th anniversary, things get out of hand, and they end up getting banned. But when they discover that an alien laid eggs in the food, they try to remedy the situation.
Gabby agrees to a babysitting job on a vacation planet despite Principal Swift's concern.
Gabby discovers that Swift was right, as she ends up on a different planet after she's been taken captive by Dranis, Jeremy's sister.