It is Founder's Day, and everyone is preparing for floats and fireworks. Jeremy, still alienated from Elena for lying to him about everything, seeks Anna's company; Anna gives him a vial of her blood and offers him the choice of becoming a vampire.
Though Damon and Alaric team up to try to stop John Gilbert from utilizing the mysterious device to kill vampires, John sets his plan in motion, leading to a chaotic, destructive, and deadly end to the Founder's Day celebration.
Tyler, Caroline and Matt are in a car when Tyler suddenly succumbs to the device being activated which generates a high-pitched hertz signal, causing him to lose control of it. Caroline is severely injured in the crash.
Tyler's father, Mayor Lockwood, also succumbs to the device signal. John kills Anna and burns many of the tomb vampires alive in the basement of an old building. Tyler's father dies along with them.
Stefan realizes that, despite everything Damon has done, he does love his brother. Elena confronts John with the knowledge that he is her father, Stefan having informed her so. Bonnie saves Stefan and Damon from John's rampage for Elena's sake but tells Stefan that if Damon kills another innocent person, she will not hesitate to take him or Stefan down.
Damon finally realizes that there is some good in him, and that he may actually want to become a better person. Jeremy learns of Anna's death; he drinks Anna's blood and overdoses on pain pills, hoping that his emotional pain will ease if he becomes a vampire.
Damon kisses a person whom he believes to be Elena, who is then invited into Elena's house by Jenna and stabs John Gilbert, who recognizes her as Katherine, pretending to be Elena. The season ends with the real Elena entering the house and going toward the kitchen, where Katherine is...
hope this helps :)
