Alliances shift and things heat up as Mystic Falls' resident werewolf proves a much more dangerous frenemy in tonight's juicy episode of "The Vampire Diaries." And thanks to the focus on Mason Lockwood and his wolfy secret identity -- the worst kept secret in Mystic Falls -- we're treated to intriguing developments that set up a much bigger showdown to come, all part of Katherine's still-ambiguous master plan.

Among the episode's better moments were scenes that reminded us why we love these characters. Caroline, fast becoming one of the series most watchable characters after spending a season as its most irritating, shows her true colors both as a friend and as a super-powered vampire when she stands up to her crusading mother. (Candice Accola also seals her place as the most bad-ass vamp on the show when she's in full veiny-eyed vampire mode, like a bloodthirsty blond angel of death.) Elena and Stefan, seemingly secure in their commitment to each other, engage in a fascinatingly layered pretend arguments that feels too real to be a complete fabrication. But one genuine argument later, they're back in harmony again, united in a love that can get them through any trial, be it Stefan's little substance abuse problem or Katherine.

And then there were the plot turns, the big reveals, the bullets, blood, and male bonding. The subtle callbacks to previous events, the clues that unveil themselves, and the minor progressions of secondary threads that suggest it's all being guided to a larger event, advancing the overall story. Something big is coming our way. For now, revel in the foreplay.

 [Full recap of Thursday's (Oct. 7) "The Vampire Diaries," titled "Kill or Be Killed," after the break…]

Flashback to boozy Florida one year ago, when we learn whose death triggered Mason's transformation.  Mason's drinking in a bar when his friend Jimmy follows him out and accuses him of going after his girl, provoking Mason into a parking lot brawl much like the one poor Carter started with Tyler a few weeks back while under Damon's compulsion. One bone crunching fight later, Jimmy's dead and the Lockwood curse has been activated; Mason's eyes starts transforming on the spot. In the present, he warns Tyler that if Tyler causes any death at all, the Wolf Man curse will be his, too. In return for telling Tyler his story, Mason demands the moonstone he's been looking for. Tyler leads Mason to his father's secret floor safe even though we know Tyler's stashed the rock weeks ago.  It's probably still in his pocket.

Under Elena's new no-lies policy, Jeremy's been filled in on the exciting Lockwood family werewolf rumor. Elena asks him to keep his nose out of the gang's investigation for his own safety, which means, of course, that he won't. Stefan and Elena share a kiss behind closed doors as they plan their day, during which they'll pretend to fight to send misinformation to Katherine's spies. They establish a safe phrase: If Stefan angrily tells Elena "I can't do this anymore," she'll know it really means "I love you." Awwww.

Meanwhile, Sheriff Forbes ditches the badge and breaks out the mom jeans for a day of quality time with Caroline. She senses a difference in Caroline but new sassy Vampire Caroline rebuffs her mother's lame sauce attempts at connecting.

It must be said that Mystic Falls throws community events/fundraisers/carnivals/beauty pageants like no other TV town since Stars Hollow. Today, for example, is Mystic Falls' Historical Society Volunteer Day, and Mayoress Lockwood is inaugurating a new park on the old Fell family property. Stefan apologizes to Mason for Damon's attempted stabbing and proposes a vampire-werewolf treaty for the sake of public safety. The nice vampire and the Zen werewolf seal it with a bro handshake.

All this supernatural business has Jeremy obsessing over Tyler from afar. Meanwhile, Amy the Matt-seeking missile warns her cute classmate Sara away from Jeremy, calling him "damaged goods." Amy is not wrong. Tyler, needing a distraction from the heavy month he's been having, invites Jeremy, Amy, and Sara to his house for some parent-free underage drinking.

At the Mystic Falls Historical Society Volunteer Excuse for New Scenery Day, Mason approaches Sheriff Forbes; now that he's met the Salvatores, he wants in on the secret council. He tells her that Stefan and Damon are vampires, which Sheriff Forbes can't quite believe. I mean, they walk in the sun! They kill other vampires! They're just so dreamy! Mason offers to prove it to the Sheriff.

Elsewhere at the park, Elena and Vampire Caroline chitchat and varnish outdoor furniture. Caroline prods for info to feed to Katherine about Elena and Stefan's relationship status, and Elena plays up her fake-real problems with Stefan for show.

"TVD" does a difficult thing here: Elena and Stefan pretend-argue about feelings they may or may not really truly have deep down inside, just to give the eavesdropping Damon and Caroline the impression that they're fighting. In another episode their argument would feel appropriate, even provide the main motivating drama -- say, if this were at the beginning of Season 2, when Elena had just found out she looks like Katherine. "How can you hate her and be in love with me?" Elena asks. "I can't do this anymore, Elena," Stefan answers -- it's his secret "I love you" code! Damon doesn't know how right he is when he unwittingly quips about how relationships are all about communication. Or does he?

Over at Tyler's underage cocktail hour, Amy apologizes for being a slut the other week. Good. Now we can feel a little bit sorry for her when she eventually dies, probably at the hands of a rage-filled Caroline. Amy's friend Sara, the one with a Jeremy crush, gets him to show off the sketches he's been working on -- but when Tyler sees that Jeremy's been on a Wolf Man art kick, he gets weirded out. In his father's study, Tyler rage-chokes Jeremy until he spills that he knows his family secret.

Back at the Volunteer Picnic Bench Painting Party, Elena is playing Caroline like a pro. She's got Caroline feeling so bad about spying on her that Caroline almost admits that she's working for Katherine. Meanwhile, Sheriff Forbes watches from afar in horror as Damon chokes on a glass of fresh-squeezed vervain lemonade, validating Mason's accusations. As Sheriff Forbes frantically calls the Council to arrange an ambush, Caroline confronts her for leaving their mother-daughter bonding day, Stefan and Damon decide they have to eliminate Mason, and everyone heads to the woods.

The Brothers Salvatore converge on Mason, but it's a trap! Sheriff Forbes and her deputies shoot Damon in the chest before shooting Stefan in a scene parallel to the one in which they first died at the Council's hands in 1864.

Oh yeah, we almost forgot that Jeremy and Tyler were having the most important convo of their young lives while the woody shenanigans were going down. Jeremy explains that he read about the Lockwood curse in his ancestor's journals, conveniently leaving out the part about vampires and magical rings and every other crazy supernatural thing that's happened to him in the past year. Tyler spills everything about his uncle, including the fact that Mason's in town looking for the moonstone that Tyler's been keeping safe. In his pants pocket! (Cue "That's not a moonstone in my pocket" jokes.) 

Sheriff Forbes and Co. haul Stefan and Damon down to the old Lockwood slave quarters, where she promises Mason they'll kill our handsome heroes. "It's the Council, not the law," she says. Spooky words from such a nice lady. Mason leaves and runs into Elena and Caroline, who've picked up the Salvatore blood trail thanks to Caroline's superpowers. Mason somehow knows that Caroline's a vampire. He threatens to break Elena's neck -- which is so TOTALLY not the Zen surfer way -- and Caroline attacks, rage-choking him against a tree. Go Caroline! It's times like these when it seems like a good idea to keep Vampire Caroline around as a friend. Caroline vampire-kicks Mason in the werewolf balls (because, all together now, Wolf Man's got nards!! High five, writer's room!) and our heroines race to the crypt to stop Mama Forbes.

Caroline stops short at the entrance to the crypt, realizing that if she interferes, her mom will know she's a vampire. Crisis of conscience! Elena flies solo, whacking her way past a cop with a 2x4, but is overpowered. Caroline races in to the rescue by biting her way through Mama Forbes' two men. (Enraged Vampire Caroline, veiny eyes and blood-soaked mouth, is quite possibly one of the most gloriously beautiful images I've seen on "The Vampire Diaries.") The revelation shocks Mama Forbes into silence, giving Stefan and Damon time to recuperate amidst the carnage. Caroline begs her mother to protect their secret, who in turn begs to be killed instead. Damon shocks everyone by opting not to kill the Sheriff after all.

Right, back to Tyler and Jeremy. Having completely forgotten the inebriated girls in the other room, the two ponder the moonstone. Tyler's totally Googled "moonstone," so he knows it's got some sort of supernatural power. He hasn't given it to Mason yet because he doesn't quite trust him. The drunk girls barge in and teasingly take it. An increasingly stressed Tyler struggles with Sara for the rock at the top of the staircase, accidentally sending Sara tumbling. Is she dead? Has Tyler triggered his curse? Here, we learn something about Sara: She's a jokester who thinks playing dead is funny. And she's totally alive. Crisis averted.

So here's the plan with Mama Forbes: Damon's gonna keep her in the Salvatore dungeon for a few days until her regular diet of vervain has left her system. Then he'll compel her to forget the whole thing. Sheriff Forbes goes along with the plan, but she doesn't want to see Caroline again; she thinks her daughter is now gone forever. Damon surprises yet again with uncharacteristic compassion, defending Caroline to her own mother.

Meanwhile, Stefan wanders over to Damon's blood bag stash like an alcoholic to a bar. Because of his vegetarian diet, he fears he's too weak and thinks weaning himself on small doses of human blood might help him get strong without triggering a relapse of his dangerous blood addiction. Stefan insists to the disbelieving Elena that human blood is the only thing that'll help him defeat Katherine. Elena is horrified.

Tyler confesses to Mason that some small part of him had hoped Sara had died earlier on the stairs so that he could realize his wolfy potential. He gives him the moonstone.

Caroline confesses to Elena that she's been spying on her because Katherine threatened to hurt Matt. They both wonder what it is that Katherine really wants. Elena and Damon have as close to a friendly exchange as Elena will allow, as she acknowledges the nice thing he did for Sheriff Forbes and he tells her what she has to hear: that Stefan will need to drink human blood. Elena goes to Stefan and gives her blessing to his plan, cutting her own hand to offer him her blood. After he hungrily drinks a few drops, she kisses his vampire face away. Oh, the things we do for love. 

Speaking of which, Mason heads to the woods for a clandestine meeting in a sports car… with Katherine! We flashback to that fateful day when Mason accidentally killed Jimmy, triggering his transformation. Katherine is there to console him, revealing to all of us watching at home that she was the one behind it all and probably compelled Jimmy to attack in the first place.

Back in the present, we learn that Katherine warned Mason to stay away from the Salvatores because he's supposed to be searching for the moonstone for her. He tells her he's got it. We recall that Katherine's the one who gave the thing to George Lockwood way back when. More importantly, we appreciate how very hard Nina Dobrev's job is as Katherine rewards Mason with a major round of tonsil hockey. So very, very hard.

Next week: The gang realizes Mason and Katherine are in cahoots, Damon appeals to Bonnie for help, and Elena gets a phone call from her evil doppelganger! Also, Damon says the line "Kill or be killed," which is the name of tonight's episode. Huh?