My Super Psycho Sweet 16: Part 3 is a 2012 MTV original film.
Two years after the events of the previous film, Skye Rotter (Lauren McKnight), is moving out of her boyfriend, Brigg (Chris Zylka), and his family's house to New York City for college with her new friend, the free spirited Sienna, (Jillian Rose Reed), whom she met on craigslist. As she is on the road, Skye receives a call from her estranged sister, Alex Bell (Kirsten Prout), who Skye has not spoken to since the past two years. Alex is surprised that Skye wasn't going to tell her that she was leaving. She begs Skye to come see her at her grandparent's country house to say goodbye before she leaves. Initially, Skye refuses, but is convinced by Sienna to tie up all loose ends before moving on with her life. Upon arriving back in Mill Basin, Skye and Sienna are greeted by a 20-something year old Nathan (Ryan Sypek), who shows them the way to Alex's after getting lost.
At the house, Nathan is asked to immediately leave the estate by two of Alex's guests: Leo (Ben Winchell), Alex's love interest, and Nico (Niko Pepaj), who is ready to have fun no matter what. Sienna leaves Skye to make sure Nathan is okay.
Skye goes inside to find Alex. After they greet Alex reveals that today is actually her "Sweet 16". Stunned and confused at Alex's actions, Skye almost leaves the party but decides to stay for a while longer when Alex becomes worried when she hears Nathan came along with them and unknowingly reveals her location to him. She then meets Ami (Onira Tares), Alex's friend who tells Skye to lose the drama. Alex tells Skye in private that she wanted her over because it is a special day for her, and Skye is the only one who could ever understand what it is like to live with the stigma from being Charlie Rotter's daughter. Brynn (Autumn Dial), a spoiled girl and Nico's girlfriend walks in on the two and is annoyed.
As day turns into night, Alex tells Skye of how she met Nathan at Zoe's funereal. He later became obsessed with her, and is willing to do anything for her love and admiration. Nico, Leo, Ami and Brynn tell their perspective of Nathan as "South Basin trash". Sienna comes in to tell Skye that Nathan must has ditched the place. After trying talking to Skye, she is forced to wait outside on the top of her car so that Alex can get more bonding time with Skye before they leave.
Brynn is outside in the back trying to make a call. When Nathan startles her, Brynn tells him that Alex will never love a freak like him. Nathan, with a knife, chases her. He then strikes a lamp post to her skull. Then her body lands in the pool. At this time, Nico looks around one of the rooms in the house. Nathan threatens Nico with the use of speakers installed in the room and has the doors electronically locked on him. Nico shoots the door with a shotgun causing everyone to worry. He unlocks the door only to find a bloody piece of clothing of Brynn's and shows it to the others. Brynn, who crawled out the pool with her brain severely damaged, walks around the house aimlessly till she crashes on a pool table, and throws up blood on Ami then dies from her wound. Everyone goes inside the room only to have all the doors and windows locked by Nathan, who has complete control over the house as he watches them from one of many cameras installed in the house.
A door near Ami opens and she runs for escape but Skye notices this is a trap and tells the others to not go before the door is closes and locks behind Ami. As she calls the cops, the police think she is making a prank call. Now panicked she runs towards the front door to escape the house. She trips and her phone falls underneath a table. While trying to reach it the police knock on the front door. When she opens the door the cop is revealed to be Nathan. He shoots her with a nail gun. In shock she runs off but is locked out of the living room where Skye, Alex, Nico and Leo are. Nathan then continues to shoot her with nails, pinning her against the door.
Meanwhile, Leo has unlocked another door upstairs. Alex and him run off for escape, leaving Skye and Nico to hunt them down. Skye gets separated from Nico when she heads into the theater room where she finds a mask resembling the one her father used. Nathan walks in and has a film playing of all the events from Skye and Alex's life. He reveals that he has known about Charlie for a long time and admires his doings. Skye calls her father sick for the things he has done. But Nathan says to her that her father was genius for murdering spoiled teenagers. She is sickened and is stalled as Nathan locks her in. Meanwhile Alex and Leo reunite and find themselves being stalked by someone in the dark. Leo points a gun in that direction and before he shoots Alex pulls a knife out and slits his throat. Alex holds the knife close in defense as she sees a man in a mask walking out from the darkness to her, who we know is Nathan. He pulls off the mask to her. Then he pulls her in and begins to romantically make out with her. As their lips part, Alex smiles. It is now revealed that Skye's little sister is the mastermind behind the horrors.
Later Nico, who is upstairs, jumps out of an opened window with a knife in hand. When he falls he is wounded by his own knife as Nathan comes out and has him murdered. Sienna, who is now frustrated from waiting waiting to long, finds Nathan hiding Nico's body. She gets help from him to start her car up, which has died out on her. As he has her checking under the hood, he continually slams the roof on her till she isn't moving any more then says this has nothing to do with her. Skye, who has managed to escape, has found a scythe in another room. She hears Alex scream and sees her crying over Leo's dead body. Skye tries to comfort her, but Alex whose face is hidden from her, turns from sad to disgust at the mere touch of her sister. Nathan shows up and becomes unconscious as Alex from behind gags her.
Skye, who is tied to a chair, wakes up to the view of a dinner table. The other seats are occupied with the bloody corpses of Brynn, Ami, Leo and Nuco. Alex is on the lap of Nathan, kissing him. Skye asks what she is doing. Alex happily replies that she is celebrating her birthday. Alex then changes drastically and admits she is hurting on the inside, suffering from the death of her parents and blames her for leading Charlie to their demise. She then claims that no one would believe Alex as the killer as she just lost her parents and has great recommendations from her therapist, whom Alex had been playing the whole time. Alex and Nathan go back to making out until Skye starts talking and plays on Nathan's emotions. She tells him that he should feel proud for succeeding in the event of getting both of the Rotter daughters in one room. She also tells him that Charlie never knew Alex had existed and would always want Skye to be protected. Unable to deny the facts he unties her. After doing so, Alex grabs the scythe and slits his chest open and charges for Skye. They duke it out and run outside.
After seeing an unconscious Sienna who has made it to the gates, Skye is chased by Alex in her brand new car, and they head into a wooded area. They fight it out till Skye uses pepper spray on Alex's face and gets up and grabs the scythe Alex carried with her. Alex taunts Skye to kill her, telling her she's just like their father. Skye strikes the scythe down to the ground, without killing her. She says, "I really wish people would stop saying shit like that" then kicks her in the face, which knocks Alex out. Skye finds that Sienna stumbling around, and is in desperate need for hospital attention. Skye sees that a police car has actually reacted to the call made earlier and drives around to check if things are well at the Bell estate. Skye is unable to get their attention in the foggy rain. Skye finds a flare in the trunk of Alex's nearby car and uses it. That still doesn't get their attention. So she then slams the stick where the gas goes and runs for cover and shields Sienna. Skye walks off, victoriously as the police have stopped to rescue them.
Time has passed since the party and Skye is now looking through a window where she sees Alex at a mental institution. Skye tells her that she wishes to go back and prevent everything from ever happening, but knows that she can't. She goes on saying that everything that happened because of Charlie Rotter has to end with them and tells her that she will always be here for her because they are family and that she truly does love her. Alex, listening and bewildered with anger, immediately slams her face into the window in a failed attempt to attack Skye. Skye finally leaves her past behind as she heads out.
Skye and Sienna are later seen at an art opening, showing off Skye's art, one based on her and Alex which displays the pain they have went through together. Skye doesn't want to stay for the opening, as she feels that this gallery wasn't for them but instead for her and her accomplishments, so she walks outside in the city streets. She is surprised as on the other side of the roads of New York is Brigg, who has came to see her from his own college to see her. He finally tells her that he loves her (when in the beginning of the film she told him not to do it during the long distance in fear that it maybe the last time she will see him again, and to say "see you later" instead). They walk off together down the road and turn a corner, showing Skye has finally received her greatest desires: Peace and Closure.
- Lauren McKnight as Skye Rotter
- Kirsten Prout as Alex Bell
- Ryan Sypek as Nathan
- Jillian Rose Reed as Sienna
- Niko Pepaj as Nico
- Ben Winchell as Leo
- Onira Tares as Ami
- Autumn Dial as Brynn
- Roy McCrerey as Brigg's Dad
- Jacob Gentry as Professor
These characters appeared in flashbacks of the previous films but the actors were not credited.
- Julianna Guill as Madison Penrose
- Stella Maeve as Zoe Chandler
- Matt Angel as Derek McNamera
- Maia Osman as Olivia Wade
- Myndy Christ as Carolyn Bell
- Alex Van as Charlie Rotter
- Chad McKnight as Party Planner
- Susan Griffiths as Chloe Anderson
- Devin Keaton as James Feldman
- Robert Pralgo as Ted Bell
- Karen, Craig, Kevin, Courtney, Molly and Lily are the only deceased characters to not appear in the flashbacks.
|1||Brynn Stone||Bludgeoned||Nathan Stillo||Bell Manor (Pool Deck)|
|2||Ami Cyrus||Shot with nails.||Nathan Stillo||Bell Manor (Hallway)|
|3||Leo Fincher||Throat slit.||Alex Bell||Bell Manor (Balcony)|
|4||Nico Velli||Stabbed and beat to death.||Nathan Stillo||Bell Manor (Back Yard)|
|5||Nathan Stillo||Disemboweled.||Alex Bell||Bell Manor (Dining Room)|
Skye Rotter, Alex Bell and Sienna Brooks survive.
- Skye: I want to say goodbye.
- Skye: I wish, i go back to stop any of it from ever happening.
- Skye: We didn't do this. He did, he started it. But has to end with us.
- Skye: I'll always be here for you, after all we're family. I love you.
- Skye: Goodbye, Alex.
- In all versions of the film, when Skye says "I really wish people would stop saying Shit like that", it is bleeped out.