On the morning of Elena's 18th birthday, Caroline is busy planning a party, but Elena is focused on searching for any clues that might help her discover where Stefan is. Damon is also searching for Stefan, while trying to protect Elena and keep her from doing anything that would draw Klaus' attention. Meanwhile, Klaus and Stefan are busy trailing a werewolf named Ray Sutton. Now working at the Mystic Grill along with Matt, Jeremy is struggling to understand why he keeps seeing the ghosts of Vicki and Anna since he was brought back to life by Bonnie's magic. Meanwhile, Alaric does his best to watch over Elena and Jeremy, while dealing with his grief over Jenna's death. Finally, Caroline and Tyler face a new and unexpected challenge.
Klaus puts a plan in motion that will give him even more power, but even with the unwilling participation of werewolf Ray Sutton, things don't go exactly as Klaus had planned. Damon and Alaric reluctantly go along with Elena's new strategy to find Stefan, leading Damon into a dangerous fight with an unexpected enemy. Jeremy turns to Matt for help as he continues to try to understand what the ghosts from his past want from him. Unaware that Caroline is in need of his help, Tyler faces an emotional confrontation with his mother.
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 uses Gloria, a witch he knew long ago, to help him track down missing information that will explain why his plan isn't working. Gloria's spells reveal intriguing glimpses of the truth, but she soon realizes she needs Stefan's knowledge to complete the puzzle. When Stefan suddenly finds himself in danger, help comes from a surprising ally. Back in Mystic Falls, a frustrating new enemy pushes Damon over the brink and he lashes out in a way that will have lasting consequences. Caroline struggles with her own emotional issues, even as she tries to help Elena face her feelings. Jeremy makes a brief but disturbing breakthrough with one of his ghostly visitors, leaving him more confused than ever. Finally, Bonnie has a strange encounter that will affect everyone.
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 unhappy 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 unhappy 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 unhappy 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.
Bonnie believes her recurring dreams about Klaus' coffins will tell her how he can be killed. The dreams also lead Bonnie to a reunion with her mother, Abby, whom Bonnie hasn't seen for 15 years. At Abby's remote farmhouse, Bonnie and Elena meet Jamie, the young man Abby took in years earlier. Bonnie's sudden appearance catches Abby off-guard, but she does her best to explain the past. Tyler turns to an unexpected ally in his quest to regain his free will. Damon is intrigued by Alaric's new friend, Dr. Fell, and Klaus continues his bitter negotiations with Stefan over control of the coffins containing his family members.
Sheriff Forbes delivers some disturbing news to Alaric and Elena about the weapon used in a recent hug. In the Salvatore brothers' escalating quest to hug 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 unhappy 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. In flashbacks to 1912, Damon recalls a beautiful vampire, Sage, who showed him a whole new way to exist. Sheriff Forbes warns Damon not to get involved in her investigation, but Damon is convinced she's going after the wrong suspect. Elena and Matt resort to breaking and entering in their search for evidence to prove Dr. Fell is a murderer. For reasons known only to her, Rebekah, becomes interested in locating one of the town's oldest landmarks. Finally, Elena comes to a new understanding of the path her life has taken, and Damon makes an emotional confession to Stefan.
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.
Damon and Stefan focus a new project that will bring them closer to destroying Klaus, and they quickly bring Elena, Caroline and Matt in on the plan. After Klaus threatens someone close to Bonnie, she has no choice but to work on the spell he needs. Meanwhile, Klaus and Rebekah find the perfect motivator to convince Finn to cooperate with them, but Rebekah is more interested in her own brutal plan to take revenge on Damon. Stefan's emotional turmoil leads him to a dangerous confrontation with Klaus and, later, to a heartbreaking moment with Elena.
Elena and Damon set off together to make sure Jeremy is safe in Denver, and to see if his special abilities can help reveal the information they need about ancient vampire bloodlines. It doesn't take them long to learn that Jeremy has been hanging with the wrong people. Stefan and Klaus both go to brutal extremes in their search for the missing weapon. Caroline is thrilled when Tyler returns to town, but Tyler soon suspects that something has been going on between Caroline and Klaus. Matt has his hands full trying to keep Rebecca busy organizing the school's upcoming 1920s Decade Dance.
Alaric finds an unexpected ally to guide him on his dangerous new path, while Damon and Meredith try to figure out what their next move should be. At the school's 1920s Decade Dance, Bonnie asks Jamie to go with her and, at Caroline's suggestion, Elena asks Stefan to be her date. Caroline is pleasantly surprised when Tyler shows up at the dance determined to sweep her off her feet, but Klaus does his best to come between them. The dance takes a deadly turn when Damon and Stefan realize they need the help of Matt, Jeremy and especially Bonnie to undo a spell that could prove devastating for everyone.
Klaus acts on his intentions to leave town with Elena, but finds resistance from a surprising new enemy. Bonnie calls on Abby to help her with a difficult spell. As events spiral out of control, Elena is determined to protect Caroline, Damon and Stefan enlist Tyler's help, while Bonnie and Jeremy take a terrifying risk to make sure her spell is effective. Damon and Stefan have a surprisingly candid conversation about the future.
Determined to protect his sister, Jeremy makes a decision that will change everything. In the harsh reality of the present situation, Elena longs for simpler times when her parents, Grayson and Miranda, and Aunt Jenna were still alive and her biggest concern was her relationship with Matt. Stefan and Damon leave Mystic Falls together on a mission, but soon split up when Elena needs one of them. Caroline and Tyler are forced to make a life-changing decision. Finally, Bonnie makes a secret deal that has heartbreaking consequences.