The sudden return of Brooke's mom threatens to destroy Mike and Jane's relationship. Nicole wants Mary Cherry's kneecap. Lily and Sugar defend school's legendary "Forever Tree", used by couples to carve their names on it, from Ms. Glass.
Ms. Glass assigns crying baby dolls to everyone in the class to teach them about parental responsibilities. Brooke must choose between her mom and her dad. Emory's wicked tween sisters hold a party and try to outdo Nicole and Mary Cherry.
Carmen runs away from home and moves in with Sam. Jane finds out she's pregnant. Brooke bonds with her new teacher, but she gets her in trouble. Ms. Glass wants to deceive her rich Aussie uncle, so she hires Nicole to play her daughter.
New student George joins the football team and Josh is afraid he's gunning for his spot. Principle Krupps wants Sam to run a story on George but George declines. Sam goes on the hunt thinking he only got on the team because of nepotism.
Ms. Glass' "love computer" pairs up her students. Harrison and Nicole manipulate the list. Harrison must hang out with Cherry, while Nicole sabotages Sam and George's relationship. Lily and Josh hook up. Mike learns of Jane's pregnancy.
Brooke and Harrison run for student council president and clash over the new random drug tests. Ms. Glass takes homeless Carmen in and helps her compete in the homecoming queen race. Oblivious Josh and Lily get high on cough syrup.
Josh must attend the autopsy of a drunk driver. Sam confronts Harrison over his prescription drug abuse only to learn that he might be dying. Ms. Glass takes on Nicole's team in the homecoming race. Carmen reconnects with her mom.
Harrison goes to a clinic for cancer treatment and gets an annoying roommate. Brooke and Sugar go to the same clinic for their eating disorders. Mary Cherry locks Sam in the Novak and forces her to write her memoirs. Carmen tries to help.
Brooke's in rehab and befriends Harrison there. He meets a doctor (played by Ann Margret), who might be God. Carmen joins a support group for teens with alcoholic parents and finds Nicole there. Josh and Lily must act naked in Equus.
Harrison's roommate Clarence passes away sending Harrison into a depression that leads to a suicide attempt and a glimpse of what life would have been like if he had never been born, by his guardian angel.
Ms. Glass gives a lecture on STDs and prepares a Cabaret-type musical on the subject. The students are to play the STDs. Sam wants to lose her virginity with George but he's not ready. Sugar and Josh hire a cool prostitute for Harrison.
Nicole learns she's adopted and tries to track down her real mother. Sugar's hurt because Josh mostly hangs out with Lily now, so George befriends him. Harrison turns into a bad boy. The girls fear he's possessed and organize an exorcism.
Mary Cherry is forced to wear "hobo sheik" clothing and hunt for food in a dumpster after her mother has financial troubles having her wardrobe seized. While Sam and Carmen have the challenge of saving their yearbook.
News of April Tuna's sudden death make everyone face their prejudices about her and finally appreciate her. Josh is inducted into the secret Mullet Society. Sam learns that Harrison loves her. The new lunch lady may be Nicole's birth mom.
Brooke and Carmen are invited under false pretenses to a predatory college party. Josh, George and Harrison try to get in uninvited. Nicole's biological mom isn't what she seems. Sam and Lily have a fun family evening with Jane and Mike.
Lilly is outraged when she realizes that even her friends are teasing the new kid who may or may not be gay. She starts an LGBT support group but everyone's against it except Harrison. Tensions in school slowly rise to a boiling point.
Nicole sets out to prove that her power is not based on her "twin set" her plan involves April, Brooke and taking down everyone who gets in her way. Meanwhile Brooke butts heads with her dad about the college guy she is dating.
The gang studies for SATs. Mary Cherry gets them to compete on a quiz show against her mother. Lily fears that Josh will make a fool of himself, since his only field of expertise is chickens. Carmen falls for her Mexican dance instructor.
Sam and Harrison claim they've spent their summer vacation in Yemen, so CDC agent Klein puts the school under quarantine in case of a viral infection. The two discuss their relationship. The rest of the gang is stalked by a masked killer.
Josh must choose between his parents' wishes and Lily. She proposes marriage. Sam and Brooke agree to make Harrison pay for the way he treated them. It backfires. The biggest girl in school challenges terrified Mary Cherry to a fight.
Sam and Brooke deliver their baby sister. Ms. Glass rents her basement to Josh and Lily, who try to face life's hardships together. Nicole tries to seduce George. Sam and Brooke make Harrison choose. The show ends on a huge cliffhanger.