Horror story plot point/glue

[Hugget Sukker]

I need inspiration for something that can link one story to future stories in a way where there is something all the stories can revolve around... Something that is not tied to a specific location, but allows travel between different areas to make sense.
So far, I have an introductory background story which can be used to base an opening story around. The protagonists look into this background matter, and they must get something out of it that leads on to the next, but before I can do that, I must have the big overarching [something] that goes on, which can be tied to this background story.

Background

John Crepse marries Danielle. Their daughter Hannah is born a large baby, albeit with an incurable heart defect. She will live till the age of 6, says Dr. Larson, who's a dear friend of the Crepses. The family goes about expecting Hannah to die. Mr. Crepse takes his anger out on Hannah, torturing her with sticks and a chain.
When she reaches the age of 5, Dr. Larson says he may be able to help them. Instead of a heart operation, Dr. Larson plants a strange disc into Hannah's stomach. Hannah lives past the age of 6, and gains the ability to levitate, which she keeps a secret.
Her birthdays upset Mr. Crepse, especially Hannah's 14th birthday. He takes his frustration out violently on Danielle and nearly kills her. Dr. Larson comes by the house to check on Hannah, but he can find no one but John. When he asks where Danielle and Hannah are, John replies "They're in the basement, both. Hannah makes it. Danielle? I beat her too. I beat her harder! I think I nearly killed her this time. Can you look at her, doc? Can you fix her?"
The basement floor is smeared in blood from Hannah and Danielle. Hannah is tied to a pillar, and Danielle lies at Hannah's feet with her head in a pool of her own blood.

Danielle: The wife
Dr. Larson: A friend of the family Crepse, who's also a doctor.
Hannah: The daughter
John: The husband

The doctor concludes Danielle is dying. It may not be possible to get her to hospital in time.
"Isn't there a quicker way?" asks John. Dr. Larson hesitantly replies, "There is, but..."
"But what?"
The doctor looks at Hannah. "The disc, I can move it, but Hannah..."
"Do it, doc. I don't mind if that brat dies."
"Er... there is a chance she can still make it."
"Then rip it out with her intenstines! Show you're capable! Show me you're more than simple men!"
Larson doesn't rip Hannah's intenstines out, but he performs a careful operation without sedation, hoping to do it in time before Danielle's heart stops.
The doctor succeeds at the disc transplantation. John orders Dr. Larson to take Danielle to the hospital, but leave Hannah. The doctor insists against it until John threatens him. The doctor obeys and takes Danielle to the hospital.
John locks Hannah into the basement, and then sits in his chair to read. Hannah screams and curses for three hours straight before she suddenly becomes quiet. After 10 minutes silence, John goes into the basement. As he reaches the bottom of the stairs, Hannah comes from behind and strangles him with the chain he used to hurt her with.
Mr. John Crepse dies from violent strangulation. His neck breaks and his air vent is crushed. 14 year old homicidal Hannah runs into the forest in a bloody night gown.

The operation on Danielle was so late that her heart actually stopped functioning. Dr. Larson did his best within the confines of Mr. John Crepse's commands, which he in no way was obliged to obey, however. No one learned of what happened exactly.
At the hospital, the doctors tried to ressurect Danielle, but had to give up. She was brought to the morgue for obduction. An obductor found the strange disc inside her stomach. It was taken as evidence material. So far, no one has been able to identify the disc-shaped device. Dr. Larson should know what it is, though, but he is denying it to the police, only telling the same story over:

"I made an extensive heart operation on little Hannah when she was 5. I was allready a close friend to the family before she was born. I know I shouldn't let friends be patients, but... ah, they just mattered to me.
I met Danielle first. She was the secretary for a professor I know, who's also my friend: Professor Surle.
Then I met John. I took him out bowling one day, and brought Danielle along, because, hey, let your friends know your friends, right. They had chemistry together, really. They quickly fell in love, and later they got married and had Hannah together, as you know.
No, I don't know where Hannah is now. Last I saw her she was with her both her parents, all unhurt. I know nothing more. And no, I don't think that John and Danielle were fighting."

My threads from this story are:

The strange disc
I decided it's invented by Professor Surle, a friend of Dr. Larson. The doctor recieved it as a gift, and it has some strange powers including life-presservation, but not ressurection.

Dr. Larson and Professor Surle
I haven't decided yet, but either they're both aliens, or they're both agents in a secret organization dealing with paranormal matters, OR both.

John Crepse
He apparently has the ability to threaten and command an alien/agent with ease. He should be something special too, but on the more bestial side of occulty. It's probably something that his daughter carries in her too. I will determine later what are these connections. Note: He's allready dead at the beginning, as you can read in the Background. But it doesn't hurt to give him a story that makes sense in the context.

The protagonists involvement will come in a casual, random manner, such as being at the wrong place at the wrong time. The obductor, for example, could be one of the protagonists.
What would you base such a story around if you were to expand it? Some principle, concept or... I'm out of ideas. I'm not good at the big picture of things. It's really my weak side: What everything should revolve around, a goal, a point. It's easy enough if you just have a haunted house. But this is away from the obvious tropes, so I'm lost.
I'll continue thinking, and if you post something, I'll post what my progress was in thinking. Thanks in advance if you can help me.

Edit: The girl Hannah, ofcourse, is another thread. What's up with her, where did she go, what's she doing, how's she going to fit in, what's she going to do, is she going to explode?

 

[Zarathustra]

Well, that strange disc is a good place to start. That's a MacGuffin, if you want. It could take the plot in literally any direction. It could be the power source to a starship. It could run off the souls of kittens. It could be a kitten-powered superweapon hidden on earth to keep it from the evil Intergalactic Lord Xenu, and Danielle could be the only person who knows how to operate it (hence the reason she must be kept alive at the cost of Hannah's life). Whatever you decide, it's obviously very powerful, very desirable, and very capable of driving any plot you want.

You've set John Crepse up to be a morally reprehensible piece of shit. If he is the sociopathic monster you portray him to be, you need to explain how he manages to find a woman who will marry him and how he can manipulate a doctor to vivisect a child. Also, how does he manipulate the doctor? The doctor sees like Dr. Mengele. Most non-sociopaths would rather die than do what he did.

Hannah could also be anything you want. Is she an innocent little girl that ends up your protagonist, is she a vengeful spirit coming back to harm those who wronged her in life, or does she turn into a bloodthirsty abomination along the lines of the girl from The Ring? You could feasibly do anything.

Who is Danielle? Why did she marry a complete and total douche? What is she going to do when she wakes up to find her husband (who almost killed her) dead and her daughter missing? What happens to her as a consequence of having the disc put in her?

Also, what kind of horror are you trying to create? I prefer the sort of horror where the "successful" hero is reduced an insane shell of a human being that writes gibberish on the walls of a padded cell in his own excrement.

A mostly sober idea

The disc is a conduit to another realm that allows otherworldly entities to enter the body of a dying person. Perhaps it was placed on earth by some alien to bring about the colonization of our universe with extradimensional terrors. Though it appears to extend life, these entities slowly take over the function of their host until it is wholly theirs. At that time, they manifest in our reality and open the door for their friends to come pouring in. Or they rape the universe with a psychic dildo. Or something else unpleasant. The details don't matter as long as they are implied to be very, very bad.

Anyway, Hannah's disc was removed at a point when she was not human enough to die, but not alien enough to transform into a soul-sucking horror from the abyss. Danielle, however, is fully human (for the moment) but the story's protagonist will slowly come to the realization that she is a ticking time bomb and must be killed to save the world. Bonus points if the protagonist falls in love with her first. Double bonus points if the protagonist is the one to kill his lover in the midst of her transformation and goes completely insane as a result. Quadruple bonus points if the disc isn't destroyed at the end of the story, but is picked up by some hapless dupe so that the cycle of horror can continue.