Blinky tries to stop a group of gnomes who are driving a car. Claire and Jim try next, but can't. Finally, AAARRRGGHH!!! is able to stop them. Jim sends the gnomes back to trollmarket while they get Señor Uhl's car back. Before they can do that, a cop pulls up and Señor Uhl gets out. He decides not to press charges. Instead, they'll serve Saturday detention with him.
Claire's mother drops her off. She comments that Claire never got in trouble before meeting Jim.
Jim's mother drops him off, thinking he did this to impress Claire. They meet up outside the school. Jim's excited to spend the whole day without the possibility of almost getting killed. They watched Steve get dropped off by Lawrence.
Uhl collects all their cell phones. They have to do homework the whole time. They may not leave the room. If anyone leaves without permission, they all face punishment. Toby starts to eat his Diablo Maximus Breakfast Burrito, but Uhl takes it.
They all struggle with being in detention. Toby notices Eli eavesdropping on their conversation about trolls and tells him to mind his own business. Steve defends him, surprising Mary. Uhl starts eating the burrito, which Toby thinks is a bad idea. He immediately starts to feel the kick. Eli tells Steve he thinks the others are't there on official business after all, meaning they gave themselves detention for nothing.
Mary is worried that the others are gossiping about her because they aren't gossiping with her. Uhl clutches his stomach and runs out of the room, leaving them alone.
Dictatious claims he's had another vision from the Pale Lady, of Gunmar being the only thing that remains. He says Gunmar will have to defeat Jim's friends before going to him. Otto says that's exactly the plan he had laid out, and that he has prepared a feast of Siamese cats, but is cut off by Gunmar. Gunmar is angry with Otto for only offering him cats and empty words. When Otto advises him not to leave, Gunmar says he doesn't take orders.
Vendel says Usurna is demanding to see Jim. She's learned about the blood goblins and gruesomes sighted in Arcadia. She also knows the bridge was left unguarded for a time during the rescue mission for Jim. She's making a case to prove conspiracy. He tells them to get Jim and find his staff. Draal goes to look for any evidence of Gunmar.
The students are starting to worry about Uhl not returning. Jim goes to look for Uhl. He hears Uhl in the bathroom struggling. Toby says the burrito was too much for him, and he could be in there all day.
They all ride bikes in the hallways, take pictures, and play around the school.
Draal finds a footprint in the woods from Gunmar. He hears a scream and follows it to a car trapped in a tree. He picks up a purse off the ground and comes face-to-face with Gunmar, who wipes his mouth after having eaten the driver. They fight and Gunmar rips of Draal's prosthetic arm. Draal uses his other arm to knock the car out of the tree onto Gunmar. It stops Gunmar only for a moment. Gunmar pins Draal to a rock and says he should have run. Draal counters with the fact that he doesn't run and is the protector of James Lake, the Bular slayer. Gunmar takes his blade and sucks out Draal's soul.
Blinky thinks NotEnrique is feeding Usurna information, but he denies it. Usurna interrupts the interrogation. She wants to talk to Jim. Blinky says he had pressing academic matters, but she gives him until sundown before they issue a warrant for his arrest.
Steve plays with a basketball in the gym. The others talk about the theft of Uhl's truck. Mary got caught making out with Tight Jeans Hank, from their rival school. They start picking on Steve for being in detention. Shannon wonders why they can't just be nice to each other. They're all going through stuff, so they act out. They're only there because they weren't smart enough to get away with it. She's in for embezzling funds from the school as treasurer. They realize it's almost 3:00, so they go back to class. Jim is stopped by Blinky, who tells him about Usurna's plans. Blinky has a plan to lie about it, but Jim wants to tell the truth. Blinky says they're the ones who plotted the rescue mission. Blinky says he'd be admitting to treason against the trollmarket. Jim stands by his actions.
The students find that Uhl isn't in the bathroom anymore. They seem him drinking milk in the hallway. They sneak around to get back to the classroom without him noticing. Mary notices that Jim is missing, but Claire says he's probably already in the classroom. Steve holds Eli back and Steve goes to do some recon.
Jim is prepared to confess everything once he's out of Saturday detention. They are surprised to see Draal in the hallway. He charges at them and they realize he's been touched by the Decimaar Blade, which means that Gunmar is definitely out. Jim activates his amulet.
Uhl is looking for more milk while the students hide in the darkness. He hears something and goes to investigate. They realize Steve is missing, but Eli says he's probably back in the room with Jim. Uhl heads back to the classroom.
Jim tries to get through to Draal, but can't. Blinky and AAARRRGGHHH!!! hold the doors shut against Uhl while Jim tries to get Draal to fight against the possession. Gunmar, through Draal, throws Jim aside, and Jim sees the mole mascot at the end of the hall. Jim says he can't fight his friend. Gunmar tells Jim that his friend is gone. Jim says they'll save Draal and stop Gunmar. Gunmar then lets Jim go, saying he wants to kill Jim with his own hands. He leaves and Blinky tells him to collect himself and get back to class.
Uhl comes across the broken lockers and chases Jim around as he tries to get back to class undetected.
Uhl gets to the room and finds Jim there. He says he heard screaming and fighting. They say they didn't hear anything. He threatens them all with another week of detention if they don't speak up. He targets Eli specifically, asking him who left the room. Eli says no one. He says he has proof they left the room and takes them to the broken lockers. Steve says it looks like a prank from their rivals. Mary thinks it was Tight Jeans Hank, and says he was pretty pissed off when she called it off between them. Uhl allows them all to leave.
Jim, Claire, and Toby talk about Draal. They don't think he's really lost. Through this conversation, Jim learns that it wasn't Toby in the hallway in the mole costume like he thought it was. Claire thinks it was Steve. They're worried about it. Krubera appear and Jim activates his amulet. Usurna then appears behind the Krubera and says he's under arrest for releasing Gunmar, breaking his oath, and treason against trollkind.
- Kelsey Grammer as Blinky
- Anton Yelchin as Jim Lake Jr.
- Charlie Saxton as Toby Domzalski
- Lexi Medrano as Claire Nuñez
- Fred Tatasciore as AAARRRGGHH!!!/Señor Uhl
- Clancy Brown as Gunmar
- Mark Hamill as Dictatious
- Anjelica Huston as Queen Usurna
- Tom Kenny as Otto Scaarbach
- Amy Landecker as Barbara Lake
- Andrea Navedo as Mrs. Nuñez
- Cole Sand as Eli Pepperjack
- Lauren Tom as Mary Wang
- Bebe Wood as Shannon
- Matthew Waterson as Draal
- Thomas F. Wilson as Coach Lawrence
- Victor Raider-Wexler as Vendel
- Jimmie Wood as NotEnrique
- Steven Yeun as Steve Palchuk
- Why everyone was sent to detention:
- Jim, Claire, and Toby were sent for "stealing" Señor Uhl’s truck (when it was actually gnomes).
- Steve and Eli got themselves in trouble on purpose because they thought Jim and his friends were on a mission, but later realize that they got into detention for nothing (until a possessed Draal starts attacking).
- Mary got detention for making out with Tight Jeans Hank, a student of Arcadia Oaks Academy.
- Shannon got in trouble for embezzling her power as the school treasurer.
- The kids all bond and have fun together throughout the entire episode. This is an interesting turn of character development for all of them, especially since they’ve all rarely interacted with each other throughout the series up until this point.
- Title: This main plot of this episode (and the title) is a spoof of the film The Breakfast Club, which focuses on a group of high school students, each members of different cliques, who spend a Saturday in detention together and come to realize that they are all more than their respective stereotypes, while facing a strict disciplinarian.
- The opening in the beginning of Saturday detention also parodies The Breakfast Club, showing panning shots of Arcadia Oaks High with the characters of the episode being dropped off at school.
- Draal is sadly possessed by Gunmar in this episode.
- Jim, Toby, and Claire briefly go through character derailment when they throw things at Eli upon noticing him trying to eavesdrop their conversation concerning Gunmar's freedom, just so he won’t find out their secret (not knowing that he already does).
- In fairness, however, and in their own defense, Eli was actually being nosy (as usual) and it really was none of his business. Not to mention the Trollhunter's sacred duty to protect their secret at all costs. Although they were talking where people could hear them.
- Uhl took the groups' cellphones, but Mary still had hers.
- Plausibility: However, this is because she had a backup phone (which is red with polka-dots).
- The entire sequence in the gymnasium appears to span 15 minutes, according to the clock. Realistically, the group conversation in the gym lasted less than five minutes.
- In several shots the kids had bikes, even though they all got driven to school.
- Plausibility: Although, they could be bikes from gym class which are supposed to look similar to Jim, Toby, and Claire's, due to budgetary concerns.
- Uhl took the groups' cellphones, but Mary still had hers.