I was too disturbed by the original idea to pursue it so I came up with a more comical derivation. Taliesin said he'd like to see them back to back, but I bet he's alone in that.
A three-year-old boy's sixteen-year-old half-sister spends summers with his family. She plays with him without condescension, imaginatively and uninhibitedly. She folds her slim frame to fit under tables and behind couches. She plays a friendly witch, a shark, a sleeping princess, a remote controlled alien robot car, and a fellow velociraptor. When she has to leave, he is devastated. Her long, blonde hair falls around him like a curtain when they hug goodbye.
Four years later, she has to take a leave of absence from college and stay with her father's family again. The boy picks up the concerned tone of his parents but is excited to live with his sister again, anyway. She arrives with her hair buzzed off, pale and dark eyed. The boy is so upset by the change he has to be goaded into hugging her.
The sister loves him very much, and is very tender with him, but she rarely leaves her room. The boy runs past her closed door as though the room were haunted.
One day, her door is open. The sister is happier than usual. She invites the boy in. He notices strange clamps and wires on her desk. She shows him how she's made tiny, one note, virtually silent musical instruments out of the wire and clamps. She uses a tuning fork to show the boy how the instrument vibrates at a certain frequency. The boy is fascinated by the object, but she won't let him take it.
Now that his sister seems happier at dinner and has her door open more often, the boy's fondness for her returns. He wants to be around her. He begins hiding in her room when she's out so he can watch her. She is totally absorbed in making hundreds of tiny musical instruments.
One day, while he's hiding in the room per usual, she shaves off all her hair. She fashions a harness to suspend herself from her closet door. She takes the tip of the wire extending from the end of her musical instrument and pushes it into her skin like an acupuncture needle. She carefully positions the instruments all over her body, including her bald head. She has to be suspended in the air because the needles are on every part of her body. The stereo is on a table by the closet. She gingerly turns on a record and has a protracted convulsive orgasm in time to the music. She passes out directly afterwards.
She wakes up to see her brother huddled in a fetal position at the foot of her bed. She shrieks, "What did you see? What did you see?" as she tears the needles from her body. The boy is terrified and runs from the room, and then from the house.
Daniel is a thirteen-year-old boy living in Berkeley. He is just beginning to appreciate the difference coolness makes in a high schooler's quality of life, and to blindly feel his way towards it. He gets to sleep in a very small in-law unit in his parents' backyard and he is pretty confident that that goes a long way towards cool.
Daniel's sixteen-year-old cousin lives in Willits. There, she is considered a musical prodigy by the Celtic musicians she's been jamming with since she was twelve. Daniel's parents offer to let her share the in-law unit when she's accepted into an all day summer orchestra program in the SF Bay Area. Daniel is indifferent at first, indifferent is cool. He is even indifferent about the pet she brings with her: a rattlesnake she caught in the hills behind her house.
Emma has a lisp and her fiddling skills don't transfer readily to orchestra music. She has long, ratty blonde hair and likes telling people about the time she milked her snake for a science project. In other words, she's not doing well socially. Daniel can see that and his indifference turns to scorn. However, she has very nice breasts and he's a thirteen-year-old boy.
Because only Daniel lived in the place, his parents never bothered to hang a door between the bathroom and the second bedroom. They prepared the place for Emma's stay by putting a large wardrobe in the doorway, so leaving one entrance to the bathroom through the tiny kitchen/entrance to the unit. Daniel discovers that he can take the particle board back off the wardrobe and spy on Emma through her hanging clothes. This way, it's possible to have best of all worlds--Emma in states of undress but no Emma in Monty Python reenactments. However, Emma is mostly preoccupied with a little craft project. Curious, one day Daniel knocks on her door to see what she's up to.
Emma is delighted to explain to Daniel how she is tuning wires to the same frequencies as the notes in Schoenberg's Pelleas und Melisande, her favorite piece. "Did you know that there are 60 acupuncture points in the foot, all relating to major organs, and there are 12 tones in Schoenberg's composition and 12 goes into 60 five times, and five is regarded as a sacred number because there are five senses and five directions and five elements? Isn't that beautiful?"
One day, Daniel watches Emma carefully sterilize her wires and, using a chart she printed out from a website, insert the wires at acupuncture points on her right foot. Then, by remote, she turns on Pelleas und Melisande on her boom box and begins brushing her finger tips over her fly in time to the music. She has a soul bearing, tearful, shuddering orgasm. Alarmed by what he's seen, Daniel knocks over Emma's shoe box of colored pencils in retreat from her wardrobe. Emma snaps to attention as she yells, "Hey, you pervert!" and unthinkingly tries to pursue him on foot, driving 60 needles deep into her foot.
Daniel's father carries Emma past him on the way to the car. She has to have a few of the needles surgically removed. "I'm going to kill you," she tells him between gritted teeth and tears of shame. Daniel believes her.
A few days later, Emma makes the family dinner--Boboli Pizza. She makes a separate pizza for Daniel, who doesn't like green peppers. Daniel refuses to eat it.
Daniel notices that the brake wires on his bike are frayed... Emma must be trying to kill him!
Daniel decides to take preemptive measures and kill Emma's snake. While Emma is at rehearsal, he uses her snake noose fashioned from cable and PVC pipe to drown the snake in a full bathtub. The drowning snake thrashes around and splashes water all over. It takes a lot of work to clean the bathroom and dry the snake before Emma gets back.
Emma's eyes are flush with accusations when she discovers the snake. Daniel's certain that she means to kill him, now.
Emma might try to suffocate him in his sleep. Daniel decides to turn off the gas to the in-law unit. The chair he keeps tipped against his door might prevent someone from saving him if she let the gas run.
Eventually, the summer orchestra intensive ends. To everyone's massive relief, Emma goes back to Willits. Daniel is unnerved when Emma offers to be pen pals. Anthrax?