When Brittany and the gang try to convince Mr. Schuester to let them do a Britney Spears number, he is reluctant to go that edgy. Meanwhile, an insecure Will is curious about Emma’s new beau, Dr. Carl Howell, so he convinces her to bring him in to talk to the kids about dental hygiene. While the dreamy doc inspires the girls to take their dental health more seriously, Will is left feeling worse than before.

The glee club works on a duet assignment, and Finn and Rachel plan to throw the competition so that Sam can have a shot at winning. Meanwhile, a love triangle between Mike, Tina and Artie develops.

Will decides to have the glee club perform “The Rocky Horror Show” for the annual school musical after learning of Emma’s newfound love for the cult classic. Despite Sue’s usual scheming, the members of New Directions inject their distinctive style to such timeless tracks as “The Time Warp” and “Damn It, Janet.”

After Finn and Sam find an unconventional way of controlling their urges, a few glee club members pick up on the strategy and start using it too. But when Coach Beiste gets wind of what they are up to, the glee club has some explaining to do. Meanwhile, the Girls vs. Boys Tournament returns, Kurt meets an ally from a rival glee club, Puck and Artie join forces and coach Beast is on the verge of quitting her job.

When Mr. Schuester gets sick, a substitute teacher takes over his Spanish class and the glee club and winds up winning over the whole New Directions clan. Meanwhile, when Sue fills in for Principal Figgins as McKinley’s top dog, she tries to flex her power on campus.

It's all about wedding and parents with Kurt getting ready for his father Burt's upcoming marriage to Finn's mom Carole, Sue decides to compete by getting married as well which will lead to the introduction of an awesome guest star: Carol Burnett. Carol will play Sue's Nazi-hunting mother Doris, who comes to visit Sue in Ohio.

New Directions heads to the big Sectionals competition to go head-to-head against the Warblers and the Hipsters. While trouble brews between some of the young couples, Emma and Carl grow closer.

It's Christmas time at McKinley High and Finn tries to get everyone in the holiday spirit; Brittany needs no help because she still believes in Santa Claus. In other news, Sue scams the teacher's Secret Santa

A local football championship game takes place and the "Thriller" mash-up is performed during the halftime show. The Cheerios, McKinley High's cheerleading team, compete at Regionals.

Love is in the air at McKinley High when the glee club sets up a kissing booth for Valentine's Day. Things don't go as planned, however, and hearts end up getting broken.

Rachel tries to launch a comeback into the McKinley High social stratosphere with a little help from Brittany. Meanwhile, Sam starts a tribute band.

Principal Figgins teaches the student body about the danger of underage drinking, and the glee club is personally touched by the message. Meanwhile, Mr. Schuester and Coach Beiste indulge in a little fun of their own.

Holly Holiday returns as the sex education substitute teacher and helps the glee club out with some new numbers. On the other hand, Emma becomes the head of the celibacy club.

With Sue Sylvester coaching Aural Intensity, Blaine and the Warblers’ dynamic set list and tough judges Tammy Jean Albertson and Sister Mary Constance, the kids of New Directions decide the only way to win Regionals is to write and perform their own original songs. Meanwhile, Quinn is hell-bent on getting Finn back and ruling McKinley once again.

The glee club agrees to help raise funds for another under-the-radar group; big decisions are made and relationships are tested.

The glee club learns about self-acceptance through the music of Lady Gaga; Lauren and Quinn compete for prom queen; Ms. Pillsbury faces with her issues; Rachel makes a life-changing decision; Santana schemes.

Sue Sylvester revives the school newspaper and decides to print a few inflammatory blind items. The glee club gains a whole new respect for Sam when they discover some interesting new information about his family life. Meanwhile, April Rhodes (guest star Chenoweth) returns to Lima and tries to convince Mr. Schuester to hit the road with her.

When the entertainment for prom falls through, Principal Figgins asks New Directions to perform at the dance much to prom coordinator Sue’s dismay. Things get heated as the competition for prom king and queen draws closer, and Jessie St. James returns.

New Directions continues to strategize their set list for Nationals with a little help from Jessie St. James. Meanwhile, an unexpected loss rocks the world of one of McKinley’s own.

New Directions heads to Nationals to compete in the ultimate singing showdown.