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 takes Stefan to Chicago, where he wants to resuscitate his sister Rebekah, who might hold the key to breaking the curse. Gradually, Stefan is reminded of his Prohibition period affair with her while still bloodthirsty himself, and its tragic end. Tyler is rightly worried, turning for an ally to her mother sheriff Forbes, about the whereabouts of Caroline, whose bully father Bill actually holds her in a dungeon for 'vampire aversion therapy' of the most flagrant kind. Katherine puts Damon on feared Klaus's trail, so he can mount a rescue with Elena after putting her in her place.

In Chicago, Katherine meets Stefan in front of a store and she tells that Elena has the necklace that belongs to Rebekah. She also feels that Stefan is plotting a scheme against Klaus, but he does not share his plan with her. Meanwhile, in Mystic Falls, Anna shows up to Jeremy and talks to him that she is alone in the afterlife. Gloria seeks out the necklace using a spell while Bonnie and Caroline visit Elena; out of the blue, her necklace burns her chest. Damon is upset with people trying to change him to be Mr. Nice Guy. Sheriff Forbes asks him to compel Bill to forget everything but Bill resists. When Damon decides to kill Bill, Caroline protects her father. Meanwhile Gloria tortures Stefan to discover who is wearing the necklace but Katherine unexpectedly kills the witch. Stefan discovers that Klaus fears a vampire hunter, Mikael, and tries to get more information from Rebekah. She's suspicious of his attitude and tells this to Klaus, who decides to return to Mystic Falls.

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.

Elena meets Stefan at the high school and he tells that he is watching her following Klaus's order. Rebekah, who is staying at the Salvatore's house, is in the same class as Elena. Elena plots with Alaric and Damon to lock Stefan in the dungeon of the Salvatore house. Tyler is fascinated and reveling in his sire bond to Klaus. Vicki convinces Matt to bring her back from the dead. Anna tells to Jeremy that darkness is surrounding Vicki, and that she has made a pact with the Original Witch. Vicki hits Matt on the head and seeks out Elena as part of her agreement with the witch. Meanwhile, Damon stays with Rebekah while Elena and Alaric abduct Stefan. Katherine awakens Mikael who confesses that he does not drink human blood, he instead feeds on vampires.

On the day of the Night of the Illumination in Mystic Falls, Mason ties Damon to a chair and the vampire believes that it is a prank of his brother Stephan. Later Mason tells that he is seeking redemption and wants to destroy Klaus to help Tyler. He goes with Damon to a cave with tunnels where it is supposed to have a weapon to destroy the Original Vampire. Elena asks Jeremy whether he may contact Lexi to learn how she can bring humanity back to Stephan, but her brother explains that he has no connection with Lexi. Bonnie goes with Caroline to the place where the witches were burnt and she casts a spell from the Grimoire to bring the dead back. Her grandmother Sheila returns and tells that she must close the passage, destroying the necklace, since the Original Witch is sending every ghost that still has pending business back to Mystic Falls. Meanwhile, the vampires from the tomb also return seeking revenge. Lexi contacts Elena and she starts Stephan's "treatment". Caroline does not find the necklace on the place that Damon told her that it would be and she suspects that Anna has stolen it. Damon can not go ahead through the tunnel that is protected and Mason goes alone. Anna returns the necklace to Jeremy and Bonnie casts a spell; Lexi, Mason, Anna and her mother, the vampires from the tomb and Sheila vanishes.

Damon, Alaric and Elena reach a hidden cage in the secret tunnel beneath the Lockwood mansion. Alaric studies the runes and primitive pictures, which indicate it was the home of an ancient Viking family, who interacted with the Original werewolf, vampires and witch. They confront Rebekah, who is shocked to tie it up with her memories of her family's youth, when their father Mikael, now the only hunter they truly dread, bullied his sons, especially Niklaus, leading in interaction with the originally friendly werewolf neighbors to family drama and the origin of vampires. After taunting Stefan, Damon releases him from Lexi's 'aversion therapy' and takes him along to seek Mikael's help. Alaric and Elena work out that Rebekah's memories don't take account of a last, crucial cruel twist.

The homecoming dance becomes the backdrop for a battle of lethal wits between Damon's party, including Mikael and Rebekah although not at all reconciled, and Klaus's, which fields the hybrids by diverting the party to the Lockwood mansion. Tyler surprises Caroline by stating he doesn't really mind being under Klaus's spell as hybrid, it's not worse than monthly lunatic agony as pure werewolf. Fearing even with the eternal oak stake in Mikael's hand Klaus may outsmart them, Damon secretly enlisted Katherine, but Klaus prepared the most stunning surprise.

Bonnie has weird dreams with four coffins. Jeremy hangs around with Tyler and invites him in his house. Stephan meets Bonnie and asks her to hide the coffins of Klaus's family. Klaus tries to force Damon and Elena to seek out Stephan and compels Jeremy to stand up in front of a pick-up driven by a hybrid in high speed without his ring; however Alaric saves him but has difficulties to recover. Jeremy kills the hybrid and he takes Alaric to the hospital with Elena. Damon meets Stephan and he tells that he saved Klaus to save Damon's life. Then Damon asks to participate in Stephan's plan against Klaus. Stephan accepts provided Elena does not know the plan. Elena makes a deal with Klaus and delivers Rebekah to him. Then she asks Damon to compel his brother to leave Mystic Falls.

Bonnie tries to open the coffin and overhears something, but Damon and Stephan arrive in the house and Damon kills the hybrid. Elena and Bonnie are preparing a birthday party for Caroline at school and Jeremy says goodbye for them. Tyler meets Caroline to tell that he would never hurt her since he loves her, but Klaus controls him. Stephan threatens Klaus and asks him to send his hybrids out of Mystic Falls and beheads one hybrid in front of Klaus to prove that he is not kidding. Klaus summons Tyler and compels him to bite Caroline, but Tyler reacts telling that he will not hurt Caroline. When Caroline arrives home, Elena, Bonnie and Matt are waiting for her; however they go to a tomb to celebrate her funeral instead. Out of the blue, Tyler appears and bites Caroline on the neck. Damon and Alaric go to a counsel meeting to raise fund to rebuild a bridge and Damon meets Klaus that tells that Stephan must stop beheading his hybrids. Meanwhile Alaric flirts with Dr. Meredith Fell and protects her against her ex-boyfriend and coroner Dr. Brian Walters. Damon unsuccessfully tries to stop Stephan from killing hybrids. Stephan abducts Elena, calls Klaus, gives her blood to her and promises to kill her, driving his car in high-speed. Klaus agrees to send the hybrids away. Klaus goes to Caroline's home and gives his blood to Caroline and saves her. Damon brings Elena home and on the next morning Jeremy travels to Denver. Alaric meets Dr. Fell while Sheriff Forbes finds Brian murdered.

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.

Now Klaus has Elijah back, they host a dinner party to negotiate a future with the Salvatore brothers, who actually procrastinate. Meanwhile combined witchcraft finally opens the mystery coffin, from which a scary surprise guest is released, but both families will be shocked. Alaric has been wounded dangerously by lover Dr. Fell, who happens to be supernatural, which makes saving him problematic, but Elena steps up. Caroline's father Bill Forbes refuses to survive his vampire bite by allowing Caroline to turn him into one like her.

Now Klaus's original family's coffins are open, he's supplanted as family head by their sorceress-maker, mother Esther, who holds a grand ball in their splendidly restored mansion. Invitations with gifts and where needed other persuades go to the Salavtore brothers, Alaric, Matt, Caroline and especially Elena, who is asked for a private meeting. After Stefan prevents Damon from stopping her, she learns that Esther, aided by son Finn, needs Doppleganger blood to put a fatal spell on her children, the others being an 'abomination' except Elijah, firstly binding their fate. Tyler prepares his return.

After starting her day with a startling discovery of Damons' 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.

Stefan still struggles desperately to get his blood-lust back under control. Damon keeps an eye on him, but has other priorities. Damon's former teacher Sage returns as his lover, in a secret pact against Rebekah, whom he seduces to keep an eye on her quest for the original white oak's sole known shoot. The old vampires are actually in league and torch the bridge made from its wood, fearing the weapon that could be made from it, but Damon stayed a step ahead. Dr. Fell tries to treat Alaric medically while Bonnie attempts to undo the curse which caused his hereditary madness, but they aren't careful enough, so Damon must intervene. Jeremy calls home from Denver, reporting that he only suffers from melancholy, but is doing well at school.

Stefan's emotional turmoil leads him to a dangerous confrontation with Klaus and, later to a heartbreaking moment with Elena. Claire Holt and Casper Zafer guest star

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 (Claire Holt) 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.