It's Elena's 18th birthday, and as she searches for Stefan, Damon tries to keep her from doing anything that might draw Klaus's attention.

Damon and Alaric reluctantly go along with Elena's new strategy to find Stefan, leading Damon into a dangerous fight with an unexpected enemy.

Klaus and Stefan arrive in Chicago, where Stefan is reunited with a vampire who hasn't really moved on from her interest in him decades earlier. In a flashback to Chicago in the 1920s, Stefan comes face-to-face with a shocking chapter from his wild past. After Damon gets a tip on Stefan and Klaus' whereabouts from an unexpected source, he and Elena follow their trail. Back in Mystic Falls, Tyler is concerned about Caroline and turns to Sheriff Forbes for help.

Still in Chicago, Klaus enlists the help of a witch called Gloria to try to discover why his plan is not working. Gloria's spells reveal some intriguing glimpses of the truth but she soon realises she need Stefan to complete the puzzle. Back in Mystic Falls, a new enemy pushes Damon over the brink with devastating consequences, while Caroline struggles with her own emotional issues.

Despite all that has happened, Caroline is determined to see that Elena, Bonnie, Matt and Tyler all enjoy a traditional Senior Prank Night before the school year begins at Mystic Falls High School. However, when uninvited guests show up, it doesn't take long for the evening to take a deadly turn. Damon convinces Jeremy that he can use his new connection to the other side to help find a way to defeat Klaus. Finally, Klaus deepens his hold on Stefan and uses him for increasingly violent and dangerous purposes.

On the first day of their senior year, Elena, Caroline, Bonnie and Matt are still reeling from recent events, while Tyler seems to be enjoying everything a little too much. Damon is annoyed by a new houseguest, and everyone is surprised by the arrival of a new student in Alaric's history class. Matt asks Bonnie for help when he realizes he made a serious mistake. Meanwhile, Stefan continues to carry out his latest assignment from Klaus.

As Mystic Falls prepares to celebrate the traditional Illumination Night, the town is invaded by spirits of the dead. After a particularly violent encounter with an angry spirit, Damon asks Bonnie to find the reason behind the ghosts' surprising power. Elena convinces Jeremy to use his connection to the other side to help her find a new way to reach Stefan, leading Jeremy to a terrible choice. Finally, Alaric discovers a long-hidden clue to the past.

With help from Elena and Bonnie, Alaric tries to decipher the meaning behind his recent discovery Elena and Rebekah engage in a mean-girl power struggle, until Rebekah finally reveals some of her family's ancient secrets and the violent past she shares with Klaus and Elijah. Damon tries a reckless new approach to make a breakthrough with Stefan, and they're both surprised by an unlikely ally.

On the night of the Homecoming dance, Rebekah opens up to Elena about why the evening is so important to her, leaving Elena with conflicting emotions. Caroline and Matt are both shocked at Tyler’s behavior throughout the evening. The night takes a surreal turn when Klaus puts his latest plan into action. Determined to outsmart Klaus, Damon enters into a dangerous partnership, leading to a terrifying turn of events.

Stefan has hidden the coffins containing the bodies of Klaus’ family, and Klaus quickly turns to violence to convince Damon and Elena that no one will be safe until he finds Stefan and gets his family back. Tyler continues to make the most of his new abilities as a hybrid, but he has to face the disturbing consequences of his actions as well. After a terrifying incident, Elena and Alaric grow increasingly concerned about Jeremy’s attitude and, ultimately, his safety. Alaric meets the beautiful Dr. Fell, who is intrigued with his amazing ability to heal. While trying to strike a deal with Klaus, Elena delivers news that truly shocks him.

Although Caroline is in no mood to celebrate her 18th birthday, Elena, Bonnie and Matt surprise her with a small party in an unusual location. Damon and Stefan disagree on the best way to handle Klaus , and a reckless Stefan decides to test his theory by taking things to dangerous extremes. Bonnie is concerned when Elena tells her about Jeremy's new plans. At a Founder's meeting, Alaric once again runs into Dr. Fell, who is in the middle of an argument with her ex-boyfriend, the medical examiner. Tyler refuses to go along with Klaus' latest demand, and is surprised when Klaus seems to accept his decision.

Prophetic dreams about the mysterious fourth coffin lead Bonnie and Elena to a surprising source, while Tyler seeks help to break free from Klaus' bond so he can be with Caroline. Alaric's new friend Dr. Fell has a secret no one sees coming, and Stefan's interference in Elena's life reveals something that surprises even him.

Sheriff Forbes delivers some disturbing news to Alaric and Elena about the weapon used in a recent murder. In the Salvatore brothers’ escalating quest to kill Klaus, Stefan turns to Bonnie and Abby, while Damon reaches out to an old acquaintance for help in setting up an elaborate plan. Intent on a plan of his own, Klaus hosts a strange dinner party, where he reveals another story from his family’s violent past until an unexpected guest brings the party to an end. Meanwhile, Caroline is heartbroken when she is unable to stop a tragedy from unfolding.

Elena is surprised to receive an invitation to a formal ball, and when Damon and Stefan hear the party is being hosted at Klaus’s newly renovated mansion, they both insist on attending the event with her. Caroline and Matt also receive invitations to the ball from unexpected admirers. At the elegant party, Elena learns of a horrifying plan that could lead to numerous deaths and she must decide who she can trust with her new information. Caroline discovers a side of Klaus no one would have suspected. Finally, after an evening of violence and dashed hopes, Damon finds a new way to cope.

After starting her day with a startling discovery of Damon’s latest indiscretion, Elena is frustrated to find that none of her friends agree with her on how they should react to the Original family’s internal power struggle. Once again caught up in the destiny of the Bennett witches, Bonnie and Abby find themselves playing a part in a ritual to appease the spirits of nature. When Elijah gives Damon and Stefan a dangerous ultimatum that puts Elena in danger, they turn to Alaric and Meredith for help with a plan that leads them to a terrible choice.

The present-day murders in Mystic Falls remind Damon of a similar crime spree a century earlier. Flashing back to 1912, Damon recalls a beautiful vampire.

A century after their first encounter, Damon and Sage meet again at the ceremony to kick-off the restoration of Wickery Bridge. Damon is surprised to learn the reason Sage has returned, and pleased when she devises an unusual method to help him figure out what Rebekah is up to. Abby is having a hard time adjusting to her new reality, despite Bonnie and Caroline’s efforts to help. When Damon informs Elena of Stefan’s latest struggles, she reaches out to Stefan to help her save a friend in danger, in hopes that it will help bring Stefan even closer to his humanity. Finally, when Damon discovers a new secret weapon, he lets Stefan in on the news.

Stefan's emotional turmoil leads him to a dangerous confrontation with Klaus and, later to a heartbreaking moment with Elena.

Caroline is thrilled when Tyler returns to town, but Tyler soon suspects that something has been going on between Caroline and Klaus. Matt tries to keep Rebekah busy.

The 1920s Decade Dance takes a deadly turn when Damon and Stefan realize they need the help of Matt, Jeremy and Bonnie to undo a spell that could be devastating for everyone.

Klaus acts on his intentions to leave town with Elena, but finds resistance from a surprising new enemy. Damon and Stefan have a surprisingly candid conversation about the future.

Determined to protect his sister, Jeremy makes a decision that will change everything; Bonnie makes a secret deal that has heartbreaking consequences.