Hexside is preparing for Grom, which happens to be a Boiling Isles version of a school prom. Underneath the school lives a monster called Grom, short for Gromethous, the fear bringer. Every year it tries to break out and a student is chosen to defeat it before it invades the town. The worst thing is Grom can read minds and shape shift into people's worst fears. Amity has been chosen for Grom Queen, which she is not happy about. Her worst fear is kind of embarrassing, and unless she can find someone to take her place she will have no choice but to go through with it. So, Luz offers to take her place as Grom Queen.
With some help from Emira and Edric, Amity starts training Luz for Grom Nite. Luz must face her darkest fears, which she claims is being looked down upon by Eda. Eda herself feels that Luz is too fragile to handle the situation and agrees to go to watch over her. Meanwhile, Gus invites King to be his co-emcee at Grom, but he is revealed to have stage fright.
On the night of Grom, everyone is gathered for Luz's battle against the Grom while at the same time having a fun time dancing. Luz is already feeling nervous, but is ready. Amity thanks Luz for doing this for her, and admits that she is impressed by her bravery. Luz enters the Grom arena and the battle against the fear demon begins. She manages to handle herself against people trapped in cat bodies and online jerks wanting to debate. But then the Grom reads her mind and transforms into her biggest fear: her mother discovering her secret of witch training. This is enough to make Luz runaway with the Grom chasing after her. King overcomes his fear and directs the students toward the fight. The Grom has Luz cornered on the edge of a cliff. Amity steps in to help Luz and her biggest fear is revealed to be rejection from an unknown recipient (privately revealed to be Luz). Together Luz and Amity dance fight against the fear demon and defeat it. They are crowned Grom Queen, and are carried away by the school as heroes alongside King.
Afterwards, Luz, who has been avoiding texting her mother, texts her back confirming that she is okay. She texts about her time on Boiling Isles without actually giving away too much, but promises to tell her more about it. When her mother tells her that she loves her "letters", Luz thinks she is talking about her texts, only to be revealed that her mother is getting letters signed by someone claiming to be Luz.
- Sarah-Nicole Robles as Luz Noceda
- Wendie Malick as Eda Clawthorne
- Alex Hirsch as King/Hooty
- Tati Gabrielle as Willow Park
- Issac Brown as Gus Porter
- Mae Whitman as Amity Blight
- Erica Lindbeck as Emira Blight
- Ryan O'Flanagan as Edric Blight
- Elizabeth Grullon as Camilia Noceda
- Bumper Robinson as Principal Bump
- Kimberly Brooks as Skara
- Dee Bradley Baker as Doctor
- Arin Hanson as Snaggleback
- Luz learns her third spell in this episode, plant magic.
- Luz, along with the illusion of her mother, speaks in her native language for the third time in this episode, following "A Lying Witch and a Warden" and "Hooty's Moving Hassle".
- "Espérate un momento." translation "Wait a moment."
- "Te extraño también, mami." translation "I miss you too, mommy."
- Someone has been sending false letters to Luz's mom.
- One of the weapons on the rack appears to be the Buster Sword from Final Fantasy VII.
- The code word for this episode is "mud".
- The Grom Tiara relic found in the Owl House video game Witch's Apprentice may be a reference to this episode.
- Through Grom, several of the characters' fears are revealed in this episode:
- Luz - Her mom finding out about The Boiling Isles.
- Amity - Being rejected by Luz.
- Willow - Ladybugs.
- Gus - Clowns.
- When Eda's portal is open it allows the transmission of wi-fi signals into the Boiling Isles.
- King is shown watching cat videos on Mewtube, a parody of YouTube.
- Dana Terrace revealed that Emira and Edric were stood up by their dates and became very jealous of Amity's "fairy tale dance".
- With the reveal that Amity has a crush on Luz, this episode marks the first time an explicitly LGBT relationship has ever been featured as a major subplot of an animated Disney series.
- In international releases, certain shots of Luz and Amity's dance are blurred out and Amity's letter is blank.