On Monday, Richard and Anais are having breakfast, when a grumpy Gumball and Darwin stomp in, splatter breakfast all over their faces, and then leave the table angrily. Anais asks Richard to hug her brothers, to which he obliges. He approaches them, and offers them a "Wonder Hug." The boys are skeptical, but he hugs them anyway, causing a large rainbow mushroom explosion in the Watterson house.
Less than two hours later, at Elmore Junior High, Miss Simian basks in everyone's misery via a closed-circuit television monitor, while playing a sad song on a cassette-player. She notices Gumball and Darwin being unusually happy, and becomes suspicious. Soon, she confronts them in the classroom, and when the boys' happiness won't let up, she fears the worst. She rushes to Principal Brown, who is caught taping himself, and she warns that there is an "outbreak of joy." He does not believe her, but Miss Simian is determined to prove its existence, taking Principal Brown's camcorder with her.
At the school clinic, Miss Simian begins her documentary recording of the purported disease, much to the school nurse's annoyance. Hours pass, and the still joyous Gumball and Darwin only get worse, and, eventually, Miss Simian isolates them in quarantine. While the nurse goes to get Principal Brown, Miss Simian observes the boys passing out from the Joy Virus, solidifying her evidence of its outbreak. She excitedly shows the rest of the school staff, and a concerned Principal Brown opens the quarantine, thus allowing Gumball and Darwin and the infection out. Principal Brown and the school nurse are immediately attacked, and infected.
Miss Simian flees to her office, and watches in horror, as the infected victims spread the Joy Virus via hugging everyone else. She wrecks her office out of despair, when she accidentally plays the same song on the cassette-player from earlier, which subsides Principal Brown's disease. She realizes the cure, and cautiously treads the halls, while avoiding the infected. She pretends to be infected herself while sneaking past the other infected people, but blows her cover when she confronts Banana Joe, who has once again violated the school dress code. The infected chase her all over school, and she successfully reaches Principal Brown's office, locking herself in. She desperately waits for the cassette-player to rewind, but it is too late, as Gumball and Darwin, who are already in the office, attack her.
Miss Simian records her final moments on Principal Brown's camcorder as she slowly gets "hugged" by the Joy Virus, saying that "this story has come to a happy ending," and laughs hysterically, while rainbow-colored liquid spews out of her mouth. After her tape ends, a brief pre-recorded clip of Principal Brown fooling around with a broom plays, ending the episode.
- Banana Joe
- Sarah (melted)
- Mr. Small
- The Sun
- Planet Cosmos
- The fourth wall is broken five times in this episode.
- The first time is when the camera hits Miss Simian's face.
- The second time is when the time-stamp knocks Miss Simian over.
- The third time is when she drags the time-stamp away.
- The fourth time is when an infected Alan passes the Joy Virus student by student, but when popped by Carmen, rainbow liquid splatters in front of the camera.
- The fifth time is when the rainbow-liquid from an infected Gumball and Darwin splatters on the camera as they infect Principal Brown.
- According to the security cameras, this episode takes place on January 16th, 2014.
- Tobias can be seen amongst the infected when Simian is locked in her office. This shows that he was eventually infected.
- This episode was originally supposed to be rated TV-PG-V in the USA. However, this was changed.
- The class photo from "The Curse" appears in Miss Simian's office.
- Darwin says "fin-flapping tastic!" like he did in "The Helmet."
- When Principal Brown and the nurse come to the room, Miss Simian does a similar dance to the one she did in "The Ape."
- This is Miss Simian's third time with a major role, the others being "The Ape," and "The Apology."
- This is the first time we see a live-action version of Gumball.
- There is a painting of an old man that resembles Mr. Robinson in Miss Simian's office. This same painting was seen in "The Painting."
- The background music played when Banana Joe walks down the hallway resembles the song "Fancy" by Iggy Azalea.
- There are possible references to the found footage horror movie Quarantine.
- The music Miss Simian plays in her office is "Moonlight Sonata," by Beethoven. It could also be a reference to the Resident Evil games because this piece of music is seen being played in some of their games.
- Miss Simian throwing jars of cough syrup on Gumball and Darwin may be a reference to the "Jarate" item from Team Fortress 2.
- Anais crying and then revealing herself to be joyful to Miss Simian may be a reference to the Witch from the Left 4 Dead game series.
- It might also be a reference to the Hardcore mode final level in the game Slender: The Arrival when the character, Kate, was also crying in the corner until she attacked.
- The clip at the end of the episode featuring Principal Brown mimicking action moves with a wooden broom is a reference to the Star Wars Kid.
- The song heard on the title page is similar to a part of "In the House, In a Heartbeat", the theme of 28 Days Later.
- The music heard when Gumball's face turns around is similar to the theme of Disney's The Haunted Mansion.
- The rainbow liquid splattering on the camera while Principal Brown was being infected was a reference to a cliché from many zombie and horror movies, where blood splatters on the screen.
- The home-camera scenes are a possible reference to the film Cloverfield.
When Gumball puts Darwin's arm on his face, it looks like the nose of Pinocchio.
- The episode uses the 24-hour clock, which is used in the United Kingdom where the show is produced, instead of the 12-hour clock, which is used in the United States, when noting time. However, the episode incorrectly attaches superfluous "a.m." and "p.m." to 24-hour clock time notations.
- Teri can be spotted in the mob of infected that discover Miss Simian, yet Miss Simian runs away from them, and Teri suddenly appears in front of her.
- According to the time that appears on the screen, the infection started spreading to the entire school after 16:36pm. However, when Miss Simian looks to the security cameras, the time shows 10:17.
- When Tina attempts to hug Miss Simian, her eyes are normal; when the mob tries to break into Principal Brown's office, Tina's eyes are missing and have two glowing red dots.
- When Miss Simian slams the door on the infected, Rocky's eyes are normal.
- In the beginning of the episode, Anais was normal, but when she sees Miss Simian walking by her on the school, she got infected. It's unknown who infected Anais later that day.
- In some scenes, Darwin has two eyelashes, but when he was infected, he has three eyelashes, like in Season 1.