Reoccurring adults

• Charles Killian – Nick Blake
• Mr Timmins – Paul Yates
• Miss Pritchard – Tanea Heke
• Mr Elder – Grant Roa
• Miss Ryder – Holly Shanahan

Other characters

• Eddie Lockhart – Rafe Custance Katie Lockhart's brother.
• Troy – Johnny Hurn A basketball player who is a friend of Te Aroha.

Kids of Room 21

All the kids in the cast are local tweens and teenagers from New Zealand. From the time of shooting the first series, the oldest was 16 (Ivana Palezevic, Tabatha) and the youngest was 11 (Georgia Fabish, Celia). All the kids appear in both series apart from Chelsea (Series 1) and Billie (Series 2).

The kids in character alphabetical order;

• Billie Anderson – Brooke Paske (Second series only) New exchange student in Room 21. Takes over Chelsea's place by having a similar personality and traits as Chelsea.
• Byron Turner – Tim Radich A skater boy. Does not listen and often takes risks.
• Celia West – Georgia Fabish A nerdy girl who loves insects and books. She is the reason everyone regained their souls in the first series.
• Charlotte Brunton – Grace MacDonald The class' "mean girl", very empowering. Has a secret love of porcelain dolls.
• Chelsea Regans – Priyanka Xi (First series only) Snotty, stuck-up girl. Bullies Celia by saying she has an 'ugly curse'.
• David White – Max Blake-Persen The first to be taken by the curse. Not much else is known about him.
• Elizabeth Ratana – Jacinta Wawatai A hydrophobic girl who enjoys kendo fighting. Te Aroha's best friend.
• Haley Bloomsfield – Zoë Robins Gullible, can be too nice and over committed.
• Jack Williams – Cameron Wakefield His great-great grandfather triggered the start of the curse. He always looks out for everyone in the class and finds a way to talk to the class from Killian's world in series 2.
• Jen de Jong – Felicity Milovanovich Shown to like sports in the first series. She appears to have a crush on Byron in Series 2.
• Johnny Campbell – Thomas Williams The class joker. He provides comic relief in dire situations.
• Karen Smyth – Frith Horan Lucy's ex-best friend. Has a crush on Will.
• Karl Bennett – Sharn Te Pou Believed there was no way to beat the curse in Series 1. Slightly selfish.
• Katie Lockhart – Beth Chote The class goth girl. Appears to also have a crush on Byron.
• Keith Wilson/Donaldson – James Shaw Bully turned nice, cares about everyone's safety.
• Lucy Myers – Liffey Jacobson-Wright A girl with phone addiction. Was Karen's best friend, but they fell out.
• Miles Delany – Brayden Muir-Mills Pessimistic, not very encouraging. Often humiliates Will.
• Owen Jameson/Slater – James Croft A computer geek. Always seen with gaming console.
• Shane Arnold – Riley Brophy Often described as a 'geek'. Was a victim of Keith's bullying in Series 1.
• Tabetha Simpson – Ivana Palezevic A girl who wants to be a director. Tries to be positive.
• Te Aroha Pene (TP) – Greer Samuel The sportiest in the class. Elizabeth's best friend.
• Will Taylor – Andrew Hampton A boy who wants to be a movie star. Appears to have a crush on Karen in Series 2.

Beginning/Possessor/Warlock

David – A janitor attempts to warn the class about Killian's curse, but David, as usual, leaves the classroom early. They heard a scream and when the whole class found David, his soul was taken, starting the curse. The appearance of the number 21 was when it was found written above the classroom door.

Celia – She was being followed by a demon who was attempting to possess her, in turn taking her soul. She defeated it by trapping it within the body of her pet cockroach then crushing it. Mr. Timmins wrote the number 21 on the blackboard after Celia answered a maths question he asked.

Johnny – He was taken to hospital when his bike crashed which he was chased by an ambulance who turns out to be a warlock who wants his fat. The warlock was killed when Johnny stabbed him with a fat injecting needle and the warlock blows up. Earlier, Johnny rode past a letter box with the number 21 written on it.

Water/Phone/Werewolf

Elizabeth – A kraken hid in the school's pipe system, so she followed it to the old swimming pool. She unplugged the drain in an attempt to defeat it but she was taken. She was eventually returned. The number "21" was found written on a cubicle door.

Lucy – She had a poltergeist in her phone, which tried to "download" her soul to Karen's phone. Lucy beat her curse by putting Karen's phone in the microwave. The brochure advertising the mobile phone said "JUST TEXT 21".

Owen – His curse was a werewolf whom he tries to defeat by locking it out, but a teacher leaves him outside to be taken. He eventually returned. The number 21 appeared as read on the calendar in the teacher's office. This Episode features Jed Brophy as the Werewolf.

Zombies/Witch/Domicile

Karen – She was in a grocery store when she was attacked by zombies but defeated them by trapping them in an oven. Karen paid 21 dollars for chocolate bars.

Charlotte – When Charlotte goes over the fence of an old house to return her necklace that was thrown over by a bully, a cat took it inside the house. Despite warnings from Jen and Celia, Charlotte went after it. She found it but its owner, a witch, took her soul before she got out. She was returned. The number "21" was carved on the fence outside the old house.

Katie – She went to her uncle's place during the weekend with her father and brother. She was attacked by a demon called Haki who can enter every nook and cranny. Her soul was taken when she mistook it for their neighbour. The number 21 was seen on a painting of demons.

Dream/Energy/Wendigo

Miles – He was forced to fight an alien in his curse. Will thought that it was his curse and escaped, however Miles was left behind therefore his soul was taken. The curse was triggered when Miles had watched 21 seconds of Will's humiliating performance.

Te Aroha "TP" – She was forced to compete against a demon in a basketball game. She defeated the demon by ripping its head off and throwing it in a waste paper basket. The curse was triggered when she bumped into a basketball player wearing the number "21".

Karl – He once doubted that there was a way to defeat the curse, but with the help of Jack he defeats a wendigo. The number 21 manifested as a carving on a tree where Karl and Jack both ride past it.

Voodoo/Mummy/Shadows

Will – In an attempt to cause Keith some pain, Karen sets up a voodoo doll that ends up affecting Will instead. It was overcome by hiding the doll in a tin with air holes where no one will find it. The number 21 was "accidentally" written in Will's blood on the doll.

Shane – On a school field trip Shane is attacked by a mummy. Shane tried to defeat it by removing its bandages but it was still invisible on the inside. He was taken. Killian set Shane 21 minutes to avoid the mummy.

Jen – Jen was attacked by a shadow demon that could manipulate the real world by moving objects' shadows. It managed to claim Jen's soul just before it was destroyed by a T-rex doll. The number 21 manifested as a shadow formed by a toy swan's neck and a candle on Jen's bedroom wall.

Vanity/Future/Vampires

Chelsea – A vanity curse made her fall apart, but it was defeated by allowing people to look at her. "21 kisses FREE!" was found written on a magazine Chelsea was reading in class.

Keith – His future self came to claim his soul and called Keith hopeless, but he went on to prove his future self wrong. The number appeared when Keith recorded his 21st day waging school.

Haley – A vampire attacked her in a blood bus. She was defeated, but eventually returned. This episode features Nathaniel Lees as Haley's demon, Mr James. The number 21 appeared when the vampire, disguised as a blood donor, offered Haley biscuits and said that she had been "so helpful, she could take... 21"

Car/Drama/Finale

Byron – He tried to escape a car demon by attempting to jump the gap across an unfinished bridge. He missed and was only just hanging on when Killian showed up. Killian gave him two choices: either he would let go and fall into a garbage truck, and he will be free if he survives, or Killian could let him up but take his soul. Byron chose the former but Killian pushed the garbage heap and caught Byron and took his soul. Byron's soul was eventually returned. "21" manifested on the demonic car's license plate.

Tabetha – She decided to make a school play about the curse. Killian summoned the ghost of the ex-drama teacher so he could get her soul but decided to take part in the play first. During the play Tabetha set up an exorcism and banished the ghost back to the spirit world. The number "21" was found on a flood light which fell onto the ground.

Jack – His soul was taken by Killian, but he was returned with the others taken. The surviving students realised that the curse could be undone by smashing a gravestone which bore the names of the students Killian had taken. After a name was smashed off that person's soul was returned and they were returned to the classroom (Room 21). After Killian's defeat, the students leave the school triumphant and ready to tackle another year at Killian High. Killian was not actually defeated.

Mechanical Demon/Giant Moth

It starts with the pupils of room 21 having an "apoplectic vision" of Killian destroying Killian High whilst in the first assembly. Jack challenges Killian, saying it is just a dream but is overpowered. Killian then says that they will all be experiencing the curse for another year, with one of them helping him. They all reawaken to be placed back in room 21. The Principal also has them sign a contract to say that they will not talk of the curse for that year before introducing Billie, an exchange student from America who is automatically under suspicion. Jack puts in a buddy system so that Killian will not get anyone on their own.

Byron – Byron is challenged by Killian and a mechanical demon to a skateboarding challenge for his soul. They use Jen as a motivator by locking her in a cage. While she escaped, he was taken. "21" was found on a dollar sign tag.

Celia and Jack – She attempts to defeat a giant moth demon by getting all the kids in Room 21 to attack it, but the Traitor turns on a torch in Celia's eyes and the moth takes Celia's soul. Jack hits it a few times then the Traitor turns on the torch again this time in Jack's eyes. Then the moth takes Jack's soul. Owen beats it. Later on Billie comes holding a flashlight, leading her to get the blame for the Traitor's misdeeds. "21" was found on a page on Celia's textbook.

Camping/Virus/Hand

Miles – Room 21 except Shane to go on a school camp, when the same demon (Werewolf Jed Brophy) from Owen's last curse shows up and attacks them. They all split up and trap the wolf, but it was not after Owen. It was after Miles, who was not helping and was back at the camp. They ran back to the camp to find him tied up and his soul taken by the werewolf's wife. Billie showed everyone Karen's rope-burned hand suspecting her to be the culprit, however it was because she pulled the rope too tightly when she was fixing her tent at the beginning of the episode. The Traitor actually tied him up. "21" was shown on Johnny's digital watch.

Shane – His curse was a computer virus that affected him in the form of living mucus while he was home sick. He defeats it after he clicks 'Destroy virus' on his computer. The Traitor is there, trying not to help Shane. "21" was found on the chat screen.

Karen – Continuing from Miles' 2nd curse, her possessed hand forces her to do bad things like hitting other students and destroying a gift from a sister school. She defeats it by pulling it off with a wood vice and dodging it so it flew out the window into a box of charity toys. The Traitor locks her in a room but she manages to escape. "21" appeared when it was written on a piece of paper by Karen's possessed hand.

Shrinking/Game/Past

Johnny – His curse is shrinking that at first attributes to his losing weight. He was knocked off a ledge where he is attacked by a larger than normal spider. The curse is defeated when he gets an allergic reaction to a bee sting. "21" was shown on Johnny's drink bottle.

Elizabeth – Her curse was a kendo video game. She and Karl attempted to play but Karl is quickly knocked unconscious, she defeated the oni that was sent after her. In the end, the Traitor attempts to take her soul but fails and retreats.

Te Aroha – Her curse was when she went back in time into the past years of Killian High. She met a spirit that warned her about three 19th-century bullies that Killian had sent. The bullies chased her onto a train where Killian asked her for her ticket, then the train pulled her into the world of lost souls where she saw Jack. The number 21 appeared when TP went past the number on a wall in graffiti.

Necromancer/Voodoo/Immunity

Lucy – Her demon was a medium possessed by a necromancer and attacked most of the girls at the library then the demon went to Lucy's house. Karen tried to warn her but it was too late. The girls had set a seance near section "012-021" in the library.

Will – He brought back the voodoo doll from his last curse (when Karen's voodoo doll affected Will instead of Keith) because he did not believe it was safe with the Traitor around and knew it still worked. The Traitor took the doll, and pulled Will's legs and arm off and put them in the school furnace. Karen managed to save the doll and sew his arms and legs back on. "21" was found on top of The Anti-Killian Meeting door.

David – His curse was on Killian's Island (a nod to Survivor). He is tripped over during the chase for immunity and all the boys blamed him to be the traitor. They voted him out and Killian took his soul. The "credits" for Killian's Island read "Room 21".

Time/Dolls/Magic

Haley – Her curse is when a time demon that can stop time with a clock that can go back or forward to any time by changing the time on it. Haley defeats the demon by snatching the clock from it and turning the time backwards to the time Haley found out about her curse and smashing it. The demon accidentally reveals that the Traitor is a girl. The number 21 was found on an encyclopedia in the library.

Charlotte – Her curse is when her porcelain dolls come to life. First she takes a porcelain doll off a girl and takes it home. The doll starts her curse. She tries to defeat them by smashing them but they shrink her. She wakes up as a doll herself, and another doll pulls her into the house and takes her soul. The number 21 was found on one of Charlotte's rulers.

Karl – His curse was at Shane's house on his birthday when the magician made Karl disappear. He then was taken to a different stage and was forced to perform the art of escapology. He was lifted into the air and dangled above a chainsaw while tied in chains. He had 30 seconds to escape but failed and had his soul removed. The number 21 appeared when the magician changed the track on the CD player to track 21.

Dead Man/Movies/Drawing

Owen – His curse was a dead man possessed by Killian who tries to take his soul during his work experience at a funeral parlor. The dead man nails him into a coffin and tries to put him into a cremation furnace, but he gets his chain and loops it over a bolt on the conveyor. The traitor, however, takes it off, so Owen bangs his coffin off the conveyor, opening it again and defeating his curse. The man had died on 21 February 2007.

Tabetha – Her curse was when she was sent into a movie by Killian and had to fight her way past a Hookman-themed demon in a stereotypical horror movie plot. She ran away from the demon into the basement. The demon started to fire shots at her and eventually hit the main circuit board allowing Tabetha to escape and defeat the curse. The number 21 appeared when she sat in seat number 21.

Katie and Keith – Her curse was when she draws a demon taking Keith's soul. The next day it comes true and her classmates get suspicious. When a two-dimensional comic demon started attacking her and gives the headmaster a heart attack, she realises she can control the demon by drawing in her book. Katie then had to shrink the demon, step on him, and burn him alive. 21 was mentioned when Katie's pens rolled together to make 2 and 1.

Reflection Demon

Billie – Billie was the last student to have to face her demon. Hers was a reflection demon that affected the real world. She confronted it in a school bathroom and it tried to take her soul. The rest of the class helped her get away. The Traitor is then revealed to be Jen, who was possessed during the first episode. Then everyone whose soul was never taken went through the portal to Killian's world. After that Killian locked them with a Latin spell and try to take their souls instead of the others, who had escaped, but eventually he disappeared when a giant rabbit (from Karl's curse) pulled him down when he was rising to go to earth and fought him. After they all looked up at the portal as it closed, rendering them trapped in Killian's world.

• Chelsea did not get a curse because she went to live with Billie's family while Billie stayed with her family.

The Traitor

In the new year at Killian High, Killian told the Room 21 students that there was a traitor among them. Billie, the new girl, was blamed.

The Traitor commits multiple heinous acts against her classmates, such as letting go of Byron after being told to, letting Jack and Celia be killed by the giant moth, taking Will's Voodoo doll, tripping David over as he was running away from demons on Killian's Island, trying to stop Elizabeth from exiting her cursed kendo game, tying up Miles, throwing Johnny off the desk while shrunken, stealing Elizabeth's phone and then using it to lure Te Aroha to the train station, letting Owen through a crematorium, locking the door when Karen is wrongly punished, locks the door of the bathroom and pushes Billie in through the mirror.

Most people in Room 21 are accused of being the Traitor, including Karen (because of the rope burn on her hand possessing it), Katie (because her drawing made Keith lose his soul), Tabetha (calling Owen making the dead man find his hiding spot) and David (because he was thought to have taken Will's Voodoo doll) just to name a few. But Billie is normally the one who gets the blame for the traitor's actions. If one was to watch closely you can tell it is not her for a number of reasons.

• The Traitor always wears a jumper (or something that hides their face), and Billie doesn't wear a jumper until the last two episodes.
• The Traitor drops a scarf in Elizabeth's curse, there is no evidence that Billie owns a scarf (All the kids in the first series wore scarfs).
• In Miles' curse, someone is seen running away from the group during their chase in the woods. Their hair is blonde, but it is not curly (like Billie's) and it is plaited. In that situation only Jen and Karen's hair was plaited.
• The Traitor has grey socks and proper school shoes (as seen in Will's curse). Billie wears white socks and ballet flats with her uniform until the last two episodes.
• Billie's skirt is shorter than the other kids' skirts and shorts. In Will's curse one can see the back of the traitor. Their skirt/shorts are down to just above the knee.

In the final episode the traitor was revealed to be Jen, although she was being controlled by a demon (that possessed her on the first episode, when she disappeared while with Byron) who would take her soul for themself instead of Killian having it. In the end when they defeated Killian with the demon from Karl's curse, the Rabbit, the whole of Room 21 was stuck in Killian's world even though he was defeated. It still looked as if they had their souls taken out as they could not get out as the portal closed.