Sorry if I copied your idea Tommy but I thought of this idea and I HAD to get it down on "paper".
I one year after the massacre at Alex's grandparetn's house, Skye has been attemding her college and is now engaged to Brigg. Sienna is having a massive 21st birthday party with Skye and her mutual friends, Kassie and her boyfriend Derek, the slightly gecky Beth, Eric, the wild blonde Amber, Nathan, Virginia and Denny. But diva Megan shows up uninvited with her jock boyfriend Chris. News of this party reaches Alex, how's currently being housed in a mental instatution. Alex can't resist this perfect oppertunity and escapes.
Meanwhile at the party (located at Sienna's rich uncle's house) Megan starts ruining the party by "accidently" spilling her drink on the stereo. Chris then takes her upstairs to the guest bedroom. With Megan out of the way, everyone starts having fun and Skye begins opening up. Alex arrives on the scene just as Eric heads outside to grab something out of his car. Alex jumps him and start beating him with her bare hands. Eric manages to escape but before he can get inside Alex grabs a itre iron laying on the ground and spears him with it. After this close call Alex heads to the kitchen to get some weapons.
The party goes on and Virginia and Nathan head into the kitchen for more booze. They start making out and suddenly Alex comes out of nowhere and stabs Nathan through the neck with a kitchen knife. Virginia screams and gets stabbed in the chest. Alex hides the bodies in the pantry and heads upstairs to kill Megan and Chris. The couple have just finished up and are laying down when Megan hears a werid noise. Chris gets dressed and goes to investigate while Megan goes downstairs. Chris enters one of the bedrooms when the door locks behind him. Alex atempts to kill him but Chris dodges her attacks. Finaly Alex mananges to shove him through the window and he falls to the ground head first.
Amber is controlling everyone's attention with her special dance in the living room and finally Kassie gets fed up and goes outside and finds Chris' body. Kassie sprints back to the door but Alex throws a vase out the window and it hits her head. Kassie falls down barely consous and Akex finsihes her off.
Alex cuts off the power from the house. The others are confused but Sienna just says there's just a power outage and as Denny gets scared Megan calls him a piece of crap. Beth gets drunk and convinces Derek to cheat on Kassie with her. The go into the bathroom and begin to make out. Alex locks the bathroom door from the outside, pours gasoline in hte window and drops a match in the room. Since the power's out the fire alram goes off and the others don't notice.
At this point Skye thinks something's up and notcies that many of the partygoers are missing. She begins searching the house for clues. She enters the kitchen and opens the pantry to find Virginia and Nathan's dead bodies. At this point Alex enters the kitchen and tells Skye its time for her revenge. Skye flees back to the living room as Alex chases her with a meat clever. Everyone in the living room screams and the fire spreads trhough the house. Everyone runs away but Alex catches Denny and hits him on the head with the cleaver. Amber sprints out the house and gets in her car and drives off.
Skye, Sienna and Megan all hide in the garage but Alex comes inside and locks the door behind her. In the pitch black Alex walks around the garage and finds Sienna. Alex knocks her out and says,"You're lucky you're the birthday girl" and then goes silent as she continues her search. Skye's hands fumble around searching for a weapon untill she finds a weed whacker. She hears footsteps and swings the weedwhacker into the approaching figure just as a cop open the garage door with Amber drove to the police station. With a light shinning everyone sees the figure that Skye hit is Megan. Magan's dead body hits the floor. The cop arrests Skye and out of nowere Alex jumps him and bashes him with the cleaver claiming,"She's mine". She then throws the meat cleaver at Amber and it hits her in the neck.
After a breif struggle skye manages to kill Alex by decpaitating her with hedge trimmers. Sienna awakens and calls the cops.
In the end it shows Brigg and Skye etting married with Sienna as one of the bridesmaid's. It zooms in on Sienna's bunch of floors hidding a knife. The movie ends with Sienna muttering about avenging her friends.
Selena Gomez as Kassie
Zac Effron as Derek
Kristen Connoly as Beth
Ryan Hansen as Eric
Anna Hutchinson as Amber
Shane Coffey as Nathan
Danielle Panabaker as Virginia
Josh Hutcherson (PEETA) as Denny
Willa Ford as Megan
Chris Hemsworth as Chris...