This is a quick outline of Season 2 of TVD, up until the point where NI's canon starts (Episode 14 ("Crying Wolf ").
Stefan Salvatore (vampire) - The younger of the two Salvatores. Dates Elena Gilbert.
Damon Salvatore (vampire) - The older of the two Salvatores. Searches for Katherine but develops a friendship with Elena.
Katherine Pierce (vampire) - Seductress who turned Stefan and Damon, and played them both in 1864.
Zach Salvatore (human) - The Salvatores' distant, distant nephew - posing as Stefan's guardian and "uncle."
Elena Gilbert (human) - a 17 year old high school girl. Her parents died in a car accident four months prior. Katherine's doppelganger.
Jeremy Gilbert (human) - Elena's younger brother, who is involved heavily in the drug scene and has a crush on Vicki.
Jenna Sommers (human) - Elena and Jeremy's quirky aunt and legal guardian.
Bonnie Bennett (witch) - Elena's friend who gradually discovers her powers as a witch.
Emily Bennett (deceased witch) - Katherine's maid in 1864. She made a deal with Damon to save Katherine.
Grams (witch) - Bonnie's guardian and grandmother.
Caroline Forbes (human) - Bubbly and popular friend of Elena. Starts developing feelings for Matt after being used by Damon.
Matt Donovan (human) - The nice guy jock who used to date Elena Gilbert before her parents died. They remain friends. Develops feelings for Caroline.
Vicki Donovan (human, turns vampire) - Matt's sister, dates Tyler. She has a crush on Jeremy, who she's associates with because of their mutual drug interests. Jeremy also treats her nice, unlike Tyler.
Tyler Lockwood (human) - Bad boy jock who is currently dating Vicki Donovan.
The Founder's Council - A secret team of townspeople who knows about the existence of vampires and protects the town from them. This council started when the town was founded and descendents of the original founders are often current members. The Salvatores (Damon eventually becomes a member), Lockwoods (member: Carol Lockwood and Mayor Richard Lockwood, Tyler's parents), Forbes (member: Sheriff Forbes, Caroline's mother), Fell (member: Logan, newscaster), Bennett and Gilbert Families are founders families.
Elena finds John Gilbert and is able to get him to a hospital in time. Caroline, also in the hospital, is in critical condition. Damon, with Elena's approval, gives Caroline his blood so she can heal. Also, Damon quickly figures out that it wasn't Elena he kissed, it was Katherine.
In light of Mayor Lockwood's death, Tyler's uncle Mason arrives to town. Tyler quickly starts displaying severe anger issues. Damon tries to investigate the Lockwoods to see why both Tyler and Mayor Lockwood were affected by a device only meant for vampires. He discovers there is something supernatural about them. Meanwhile, Stefan threatens John and orders him to leave town. John obeys, giving Jeremy his ring before leaving.
Katherine, pretending to be Elena, makes a fuss at the mayor's wake and later shows up at the Salvatore house to meet Damon. After some antagonistic banter, they make out. Damon stops and says that he'd be willing to start fresh if she'd just tell him the truth. She then confesses that she never loved him and leaves. Katherine goes to the hospital where Caroline is healing and smothers her with a pillow, turning Caroline into a vampire.
Later, Elena finds Damon in her room drunk and upset. He tries to convince Elena that there is something going on between them and tries kissing her. Elena refuses, insisting "I love Stefan, it's always going to be Stefan." Jeremy comes in an interrupts, and Damon impulsively snaps Jeremy's neck, killing him. Elena discovers that the ring John Gilbert gave Jeremy saved him.
At a carnival event, Caroline struggles maintaining her vampire urges and Stefan offers to teach her how to handle bloodlust. Matt later on confesses his love for Caroline, despite her acting "weird" around him.
Later Alaric has a theory about what the Lockwoods could be - werewolves. Isobel had done reseach about them at Duke university, so he, Damon and Elena decide to visit her office there. Stefan stays behind to help Caroline. At a party, Stefan, Caroline and Matt get chased by a werewolf, later revealed to be Mason. Tyler discovers this as well.
On the trip to Duke, Elena is still mad at Damon for attacking Jeremy. Still, they find out that there is an aztec curse that binds werewolves and vampires to the sun and the moon. Only when they return does Elena ask if Damon knew Jeremy was wearing the ring before he killed him. Damon admits that he didn't and was sorry. Elena tells him that Damon had lost her for ever and they were not friends.
The next day, Jenna throws a BBQ and Damon, Alaric, and Mason, who Jenna knew in high school, attends. Damon takes this opportunity to see for certain if he's a werewolf and kill him once he does. Mason catches on quickly and, privately, insists to Damon that he means no harm. Damon doesn't buy it and later on, tries to kill him with a silver knife, but it doesn't work. Mason tells him then that he now has an enemy.
Meanwhile, Katherine compells Caroline to keep Elena distracted so she could spend time with Stefan. Stefan stabs Katherine with vervain and ties her up, demanding answers about why she's in town. She reveals that George Lockwood rounded up the vampires to be burned in 1864. She made a deal - George can burn all the vampires, but she'll give him the moonstone - an amulet that Mason is now looking for - if he arranges Katherine's escape. She also insists that she did and still does love Stefan, and that she never compelled his love for her. Katherine threatens that if Stefan doesn't break up with Elena, she'd go on a killing spree. Stefan and Elena decide that they would pretend to "break up."
Tyler demands answers about this whole werewolf business and Mason tells him that a year ago, in a fight, he accidentally killed his friend Jimmy. We later learn that people with the 'werewolf gene' don't become full fledged wolves until they kill a human.
It is volunteer day for a town event, Mason tells sheriff Forbes that Damon and Stefan are vampires. Damon drinks vervain-spiked lemonade which causes both bothers to realize they've been revealed. When they try to take Mason out, they are ambushed by Sheriff Forbes and her police force with wooden bullets and vervain. With Elena, Caroline tracks them down and stops the Sheriff from killing them. Caroline reveals she's a vampire to her mother in the process, and Forbes does not approve. Surprisingly, although clearly tempted, Damon doesn't kill the Sheriff because she's his "friend." Instead, they wait until the vervain is out of her system and Caroline compells her memories away of the incident.
Bonnie has a vision, discovering Mason is in a relationship with Katherine. He's is looking for the moonstone for her. Damon, Bonnie, and Stefan then conspire to capture Mason to see what he knows about the moonstone. Bonnie uses magic to discover that Mason is hiding the moonstone in a well. While Elena and Stefan go searching for it, Damon tortures Mason (with wolfsbane) for information. He finds out that the stone is supposed to break the sun and moon curse - allowing either vampires to walk in the sun or werewolves to turn whenever they want. Damon tells Mason he's being played by Katherine before he kills him.
Meanwhile Stefan and Elena find the well and Stefan tries to retrieve the moonstone. However the well is full of vervain. Elena helps him out and also retrieves the moonstone. Later, Damon uses Mason's phone to get people to believe Mason left town again but also finds Katherine's number. He calls her up to antagonize her and gloat that he killed Mason, but Katherine insists she has a plan B.
Elena, now at home, gets a call from Katherine. Suddenly Jenna tries to kill herself with a kitchen knife. Katherine apparently compelled her. Jenna now in the hospital, Elena makes the decision to truly end her relationship with Stefan. Damon is apologetic but Elena insists that "Katherine won." Katherine apparently needs a werewolf for her plans, so she compells Matt to pick a fight with Tyler at the Masquarade Ball coming up.
The day of the ball, Katherine confronts Caroline and gives her a message to send to the Salvatores: "Tell Damon and Stefan that I want the moonstone, or I will rip this town apart until it rains blood." She says the exchange must happen at the ball. Both brothers agree that instead of complying, they'll try to kill her. They enlist the help of Bonnie, Jeremy, and Alaric.
Meanwhile, Katherine prepares for the ball by dressing up as Elena and meets up with her ally Lucy (a witch). Lucy has clearly agreed (even if not by choice) to help Katherine get the moonstone. She is prepared for Damon and Stefan to put up a fight.
At the ball, Jeremy helps Bonnie produce a spell similar to the tomb spell that locked the vampires under the church. It is clear both Jeremy and Bonnie are getting closer. Meanwhile Lucy discovers that Bonnie is involved in this and isn't happy. They are cousins. She later meets with Bonnie and convinces her to hand over the moonstone and to trust her.
Alaric and Elena do not attend the ball so they can look after Jenna. However, Elena realizes everyone is keeping something from her. She figures out Jeremy is there so she sneaks out to the Ball. At the event, Jeremy talks with Katherine, telling her that the Salvatores are ready to meet her. When she leaves, that is when Elena finds him and demands to know what's going on.
Caroline finds Matt and Tyler fighting in a room with two other girls. Caroline knocks out Matt with amazing strength and Tyler is shocked. However one the girls is also compelled to fight Tyler if Matt doesn't succeed. He pushes her back and she hits her head hard enough to be killed. Tyler is now a werewolf. Caroline helps Tyler cover up the accidental murder.
Katherine goes to the meeting place only to find Caroline. Caroline manipulates Katherine into a spelled room where no vampire can get out. Damon and Stefan are in there as well and attack. It is not an easy fight, Katherine much stronger than both brothers. Outside, Elena is with Jeremy and Bonnie and inexplicably, severe wounds start to appear on Elena's body. They discover Katherine, with the help of Lucy, linked Elena to her. Every wound the brothers inflict on Katherine is inflcted on Elena. Jeremy rushes up to the room and tell the brothers to stop fighting her because they're hurting Elena.
Until they figure out how to despell Katherine and Elena, the Salvatores are stuck in the room with Katherine. Katherine brings up memories of how they were all together in 1864, clearly rubbing in the fact that she prefers Stefan. Stefan discovers that Katherine must've been running from someone back then, but Katherine distracts them both from answering those questions. Soon Lucy shows up, hands over the moonstone but incapacitates Katherine with her magic. She also removed the spell on Elena. Damon takes her to the tomb that was underneathe the church. She's trapped by a new spell. Before Damon entombs her, she insists that Elena is in danger but refuses to say why. So Damon locks her inside along with the moonstone.Elena is captured by an unknown man outside of the Lockwood house after having a heart to heart with Stefan about their relationship.