[For a refresher course on Season 1 - go here]
Episode 1: The Return
Katherine has returned, is impersonating Elena, and tried to kill John Gilbert. Caroline is in the hospital after the car accident and Damon has given her some blood to aid in her recovery. Tyler's uncle Mason has come back to town after the death of his brother (Tyler's dad). Katherine tells Damon she never loved him and only ever loved Stefan. Damon tries to kiss Elena and she basically tells him the same thing. He snaps Jeremy's neck but he's safe because he was wearing John's ring. Katherine kills Caroline - who has Damon's blood in her system - and tells her to give the Salvatores a message "Game on".
[For a full recap of episode 1 and 2 of Season 2 - go here]
Caroline wakes up in the hospital as a confused vampire and feeds on a nurse. Tyler's uncle Mason is looking for a family moonstone. Damon compells a guy at the carnival to pick a fight with Tyler in order to provoke him (so they can figure out what he is) but Mason breaks it up with superhuman strength (werewolf!) Then Caroline drains the poor guy. Bonnie blames Damon and Stefan promises to help Caroline.
Episode 3: Bad Moon Rising
Elena, Damon and Alaric look into Isobel's research on Katherine and the Lockwoods. Stefan teaches Caroline how to be a better vampire and
and Caroline, but Tyler stops them. Caroline breaks up with Matt in order to protect him from herself.
Episode 4: Memory Lane
Caroline is forced to follow Katherine's orders. Stefan tries to give Katherine vervaine but she reveals that she's developed an immunity to it. Damon stabs Mason with a silver knife, but learns that the whole silver-kills-werewolves thing was just a myth. Oops. No one will die the way they're supposed to! Katherine gives Stefan and Elena an ultimatum: she will kill everyone Elena cares about unless they end their relationship so they pretend to break up.
Episode 5: Kill or Be Killed
Elena and Stefan continue to be fake-broken up. Mason tells Sheriff Forbes that the Salvatores are vampires. Caroline and Elena save them, but now Caroline's mom knows she's a vampire. Caroline apologizes to Elena for spying on her for Katherine and explains that she did it to protect Matt. Tyler almost kills a girl by accident and learns of the Lockwood curse (if you kill someone, you become a werewolf). He gives him the moonstone and we learn that Mason is in cahoots with Katherine.
Episode 6: Plan B
Jeremy offers to help Damon get rid of Katherine. Caroline's mother is compelled to forget that Caroline is a vampire. Bonnie helps the Salvatores get Mason. They torture him for information and then kill him. They find the moonstone but it's buried in a well full of vervain. Katherine compells Jenna to stab herself and compells Matt to attack Tyler so Tyler will kill him and trigger the werewolf curse.
Jenna lives. Alaric keeps an eye on her and Elena while everyone else (Bonnie, Jeremy, Caroline and both Salvatores) go after Katherine at the masquerade ball. Katherine is there pretending to be Elena and she has her own witch to help her, Lucy. Matt picks a fight with Tyler, but Caroline breaks it up. But of course, Katherine had a backup plan compulsion, so drunk girl Sara tries to stab Tyler and he accidentally kills her. The werewolf curse is on! Elena, never one to be left in the dark, goes to the ball to find out what the heck is going on... Stefan and Damon try to kill Katherine, but she's been magically linked to Elena so everything they do to her Elena also feels. Jeremy gets them to stop and Bonnie confronts Lucy, who cast the spell. Turns out Lucy is Bonnie's distant cousin and she agrees to lift the spell and causes Katherine to collapse. She wakes up locked away in the tomb, where she was supposed to be all along. She warns Damon that Elena is in danger and then wouldn't ya know it, she's kidnapped by someone.
Episode 8: Rose
Jeremy tells Stefan that Elena is missing. She's been kidnapped by two vampires named Trevor and Rose, who intend to give her to an 'original' vampire named Elijah. It turns out she is the Petrova doppelganger and the key to breaking the curse that keeps vampires from going out in daylight and makes werewolves only able to change on the full moon. Trevor had helped Katherine escape the originals many years ago and he and Rose have been running from them ever since. Tyler gets Caroline to tell him what's going on with his newfound abilities after Sara's death. She tells him she's a vampire. Bonnie casts a spell to find Elena and the Salvatores go off to rescue her. Elijah kills Trevor and compells Elena to tell him where Katherine and the moonstone are. Damon stakes Elijah and they get Elena home. Rose warns them that Klaus, the oldest of the originals, will be coming after Elena. Damon admits to Elena that he loves her, then compels her to foget and puts her vervain necklace back on her. PS: Surprise! Elijah isn't really dead!
Flashback to Katherine in Bulgaria in 1490 giving birth to a baby girl. Her family takes the baby away and says that she shamed her family. Back in present time, Elena is at the tomb with Katherine trading blood for information. Turns out Katherne was a Petrova doppleganger, which is why Elijah wanted to kill her and break the curse. Trevor helped her escape and she used Rose to become a vampire. They've all been on the run ever since. In order to break the curse - which is why Katherine really came back to Mystic Falls, to get Klaus off her back once and for all - she needs a doppleganger, a witch, a werewolf, a vampire, and the moonstone. (Elena, Bonnie, Tyler, Caroline, respectively.) Bonnie meets Luca, a male witch (warlock, ugh) and his father who are secretly working for Elijah.
Episode 10: The Sacrifice
Stefan and Damon try to get the moonstone from Katherine and Elena tricks Rose into bringing her to Elijah, so she can surrender (to protect the others from Klaus). Bonnie tries to lift the spell on the tomb and incapacitate Katherne so Stefan can get the moonstone. She channels power from the warlock she met, but it's still too much for her. Jeremy fucks up the plan further by going into the tomb where Katherine tries to feed on him. When Stefan goes to save him, he gets stuck in the tomb with her (being a vampire and all!) Caroline helps Tyler learn more about what to expect from his first full moon transformation. They find Mason's diary and a video and needless to say, Tyler is freaked. Jeremy and Bonnie almost kiss. What!? Damon saves Elena yet again, but Elijah shows up with two other vampires who are ready to take Elena to Klaus. Instead Elijah kills them and lets Elena, Damon and Rose go. Hm, why?
Episode 11: By the Light of the Moon
Elijah shows up to make a deal with Elena. He reveals that he no longer works for Klaus and wants to prtect her from him (eventually he'd like to use her to bait him to kill him). He frees Stefan from the tomb and agrees to keep Elena and her friends/family safe. Caroline goes back to Tyler the next morning and helps him deal with the night before. Luckily he didn't get out and didn't hurt anyone. Damon lets Rose stay with him, but Jules (as a wolf) attacks them. She bites Rose's shoulder and they orginally think the wolfbites-kill-vampires thing was a myth, but later they realize her shoulder is all infected. Ick!