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.

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.

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.