Season 2
Dubbed "Season of the Kat", Season 2 picks up directly where Season 1 leaves off. After Katherine Pierce stabs John Gilbert, Elena Gilbert walks into the kitchen to find John on the floor, severely wounded. Katherine leaves before Elena sees her and she calls 911 after checking on Jeremy Gilbert. He wakes up but is not in transition as he had hoped. Stefan Salvatore says that he didn't take enough pills, so Anna's blood simply healed him.
Elena goes to the hospital to see Caroline Forbes and also runs into Bonnie Bennett and Damon Salvatore. Damon agrees to give Caroline blood to heal her since she's not doing well. Jenna Sommers appears and she and Elena have a confused exchange that results in Damon realizing it was Katherine he kissed. Stefan and Damon confront each other about the fact that Damon thought he kissed Elena, and Katherine says she's come back for Stefan, which he doesn't believe.
Katherine coldly tells Damon that she never loved him. Damon confronts Elena about his feelings for her and the feelings he thinks she has for him. While Elena admits she cares about him, she says it's always going to be Stefan, which is basically the same thing Katherine told him. This sets him off and he snaps Jeremy's neck. Fortunately, he's wearing John's ring and comes back. Mason Lockwood, uncle of Tyler Lockwood, is also introduced. Katherine turns Caroline into a vampire.
Bonnie has a hard time with Caroline becoming a vampire, and Damon tries to kill Caroline, thinking she'll become another Vicki Donovan. However, Elena and Stefan stop him and Stefan begins helping her with the transition. Damon spies on Mason and Tyler, trying to figure out what's up with their family. He, Elena, and Alaric Saltzman do some research to try to find out more about the Lockwoods. They come across information that suggests werewolves exist and that one bite from one can kill a vampire.
Stefan teaches Caroline how to cope with being a vampire. She slips up and bites Matt Donovan, which later results in Caroline intentionally getting Matt to break up with her so that it doesn't happen again. Tyler discovers that Mason is a werewolf. Stefan gets information from Katherine about the Lockwood men having the werewolf gene, and that she faked her own death back in 1864. Mason tells Tyler that to activate the curse, you have to kill someone. Stefan and Elena figure out that Caroline is "working with" Katherine and they stage pretend to break up to appease Katherine's wishes.
Mason goes to Liz Forbes and reveals to her that Damon and Stefan are vampires. She and a couple of deputies capture them. Caroline saves them while having to reveal to her mother that she's a vampire. Caroline tells Elena that she was only working for Katherine because she threatened Matt's life. Stefan decides to start drinking a little human blood each day, and Elena offers her own blood. After receiving the moonstone from Tyler, Mason tells Katherine that he has it, revealing that they're working together.
Jeremy relays everything he learned from Tyler to Damon, but when Jeremy tries to get the moonstone from him, he's told Tyler no longer has it. With the help of Bonnie, Damon captures Mason. After talking with Caroline, Liz promises to keep it a secret, but Caroline compels her anyway just to be safe. After finding out the location of the moonstone, Damon kills Mason. The others find and retrieve the moonstone and Damon calls Katherine to taunt her. She retaliates by having Jenna stab herself, but she survives. Elena then breaks up with Stefan for real, not wanting anyone else to get hurt. Tyler thinks that Mason just took off.
The gang--minus Elena--gets together to plot Katherine's demise. While they don't kill her, they do end up trapping her in the tomb. Meanwhile, Tyler accidentally kills a girl, triggering the curse. Elena is kidnapped by two vampires, Trevor and Rose. They want to offer the doppelganger to [[Elijah], a powerful vampire. They've been running for 500 years and want their freedom. Elijah kills Trevor but lets Rose live. Damon and Stefan show up and save Elena, and they also drive a large piece of wood through Elijah's heart.
Rose shows up at the Salvatore mansion and offers to help Stefan with a vampire who's going to be coming for Elena--Klaus. Damon confesses his love for Elena but compels her to forget. Elijah wakes up and pulls the wood from his chest, revealing that he can't be killed through normal means. Caroline tells Tyler that she's a vampire and they bond over their similar situations.
Elena gets information from Katherine about her past, including the fact that Katherine had a baby before becoming a vampire. The sun and the moon curse can only be broken with the blood of the doppelganger, which is why Klaus will be coming for her like he did with Katherine. Bonnie meets Luka and Jonas Martin, who are both warlocks, and Jonas happens to be working for Elijah. Elena uses Rose to try to find Elijah and give herself up to him but Rose calls Damon, who interrupts. Elijah still shows up, but leaves them alone. Stefan gets trapped in the tomb with Katherine after saving Jeremy. Caroline helps Tyler with his first transformation. Jules, a werewolf and a friend of Mason's, shows up and wonders where he is.
Rose steps in front of Damon when Jules--in werewolf form--attacks them, and she gets bitten. Elena forms an alliance with Elijah. Stefan tries to find Isobel to get information about Klaus, but he finds John instead. Rose slowly dies, and Damon is more emotional over it than he would like. After being pushed by Elena to embrace his humanity, he goes out and kills a girl. Caroline becomes a bit torn between Tyler and Matt. Jules tells Tyler the truth about Mason. Jenna learns that John is Elena's real father. Stefan tries to talk to Tyler while Jules and a friend of hers named Brady kidnap and torture Caroline. They agree to exchange her for Tyler. Damon and Stefan fight a group of werewolves and Jonas shows up to help. Tyler helps Caroline but does so after hesitating.
He apologizes later but Caroline won't hear any of it, and he then teams up with Jules and Brady. John gives Damon a dagger that will supposedly kill an original vampire. Damon is also introduced to a woman named Andie Star, who he feeds on and compels not to tell anything. Stefan and Elena go to her parents' lake house to get away, and they discover council stuff (weapons and journals) in a hidden closet. Brady and Tyler attack them, but Stefan tells Tyler the truth about what's going on and Tyler apologizes for his involvement. Stefan kills Brady. Jules and other werewolves torture Damon for the moonstone but he won't give it up, and Elijah saves him. Tyler then leaves Mystic Falls with Jules. It's revealed that part of Elijah's plan involves Elena's death, and she's willing to do it anyway.
Elena reads through Jonathan Gilbert's journals and finds stuff about Stefan, and he admits to having been quite the evil vampire back in the day. Damon, with the help of Alaric, makes a plan to dagger Elijah. It's discovered that a vampire can't do it or they'll die, so Alaric does it instead. However, they pull the dagger out after Elijah "dies", and he's revived. He finds Elena and she tricks him and manages to dagger him herself, and this time, they leave the weapon in his chest. Jonas takes Bonnie's powers away from her as a punishment for using his son for a spell. Katherine shows up suddenly, released from the tomb. She claims she wants to help the gang.
Stefan tries to get Jonas and Luka on their side but they don't go for it after learning of Elijah's defeat. Instead, they do a spell that ends up getting Luka killed. Jonas attacks the others out of revenge, but he's killed by Katherine and Stefan. Right before he dies, he gives Bonnie her powers back along with knowledge of how to kill Klaus. Elena also gives Bonnie her blessing to date Jeremy. Matt learns the truth about vampires and freaks out. Jenna also learns that Isobel is alive when she shows up at the house, and that Elena knew about it, which tells her that both Elena and Alaric had been lying to her all this time. She goes to stay at college for a few days.
Bonnie, Jeremy, and Damon check out a spot where a hundred dead witches were killed so that she can harness the power in order to kill Klaus. Isobel kidnaps Elena with the help of Katherine, but it's a set up. Maddox, a warlock working for Klaus, takes Katherine hostage. Isobel, meanwhile, kills herself in front of Elena after being compelled to do so. Matt asks Caroline to tell him everything, and after she does, he asks her to compel him. However, it's a trick, and he actually reveals all of that information to Liz. Maddox transfers Klaus into Alaric's body. After learning that Klaus is in town--albeit not knowing he's in Alaric's body--the gang forms a plan to take him out at the school dance. Jeremy ends up telling the others that if Bonnie does this spell, it'll probably kill her.
Bonnie and Damon then come up with their own plan. Bonnie fakes her death to make Klaus think she's no longer a threat, so that she can still be used when they need her. Elena then undaggers Elijah without anyone else's knowledge.