I'm supposed to be on holiday... Got a plane to catch in a few hours...
So I rushed this one a bit, I hope it turned out ok.
See you in three weeks!
This is an entry for Finish the Story Contest - WEEK #26.
Here is 
The moonlight descended on the east side of the Wagner Tower like an ancestral bone dust. The ectoplasm of a vague awareness crossed a tenant’s mind seeking for oblivion: finally, the dull blows coming from God knows what remote corner of the old building had decided to quit and he would have slept. However, between the seventy-fifth and seventy-fourth floor, a particularly fine ear could have still seized an intermittent, stifled counterpoint of voices.
"I feel that this unusual condition is helping us bring out some interesting perspectives, Mendo." In breaking the silence, the psychotherapist's voice had soon lost its initial momentum.
"..."
"I want you to know that this time won’t be billed, go ahead if you feel like it." She tried to assume a playful expression. Hidden underneath her short suit jacket, Dr. Wallace's fingers were nervously playing with a fluorescent orange rubber bracelet.
"No-one is ever suspended, not even now with seventy-four floors of nothing underfoot..."
"Well, this is certainly a positive observation..."
"Shut up, you don’t know a shit." An almost calm remark, pronounced with a firmness that hit Dr. Wallace like a bucket of frozen water.
"Have you ever thought, doctor," Mendo continued, sharply spelling out his last word, "that the fear of emptiness, the horror vacui as they defined it in the Middle Ages, is nothing but the unconscious and desperate attempt to look away from the ultimate truth?"
Since the elevator had blocked its descent, the patient had confined himself to a corner on the opposite side of the entrance. His left leg was now dancing grotesquely, animated like it had a life of its own and in contrast with the cadaveric stiffness of his other body parts.
"I never thought of that." Dr. Wallace wisely responded in brief, observing for the umpteenth time the assistance number carved on the elevator control panel.
"Mmmm..." A growing moan on the other side of the narrow cabin.
The doctor instinctively thought of her daughter that night, when the wind had hit the fixtures of the old house in the mountains so intensely that it produced an endless banshee howl. The little girl had made a sound of compressed horror, just like that.
If only she had known, she would have never asked Mr. Anatoliy "Mendoza" Volkov, an extraordinarily subtle personality, to follow her downstairs after that emergency therapy session in her office. On the other hand, he was one of her first and most challenging patients. Furthermore, he used to pay awesomely.
"Because the void swarms." Now his eyes were on the doctor, sunken out and bugging out at the same time.
"Soon they'll free us, do you think you'll keep writing that song you were talking about?" Dr. Wallace ventured. She realized that the silk shirt was soaking with her acrid sweat.
"It's the Yellow King's dominion, he comes from the void, it's him who made me do those things. I did not want to." His whine ripped open in a sinister vocal of terror.
"Mendo..." She did not know what to add. Now the doctor's hand, behind her sweating back, was pressing the assistance button convulsively.
His wide open eyes. They had stopped staring at her and now they were pointing up, right behind her shoulders.
"Mendo, what's up?"
"The Yellow King. He's here."
And this is my ending:
Sitting in the interrogation room, she looked intensely at the steaming cup of espresso on the table before her. Gingerly, she picked it up. She closed her eyes as the black liquid made everything alright again.
Finally, she smiled at the aged Detective seated opposite her. He smiled back. "Let's go over the facts again," he said.
Dr. Wallace nodded. "Volkov had asked for a therapy session outside my working hours. It wasn't the first time. He seemed... Distracted, as if waiting for the meeting to end. I did not notice that he'd stopped taking his meds. It became apparent only later, in the elevator."
The Detective studied some papers. "Whose controls had been tampered with."
She shivered. "He ambushed me, didn't he? All that talk about the King in Yellow--"
He scoffed. "Somebody's been bingeing on True Detective."
She shook her head. "Not Volkov! He was something of a recluse. Home-schooled, no TV, no internet. He claimed they blocked his inspiration. That's why he needed me. His insulation from anything he didn't accept, left him... Impressionable..."
"Left him dead, too." The Detective stood up. "We're done here. You will be tested for occult contamination, then we'll escort you home... Take a couple days off, spend them with your kid."
The Assistant DA entered the room. "Briscoe said you have something for me."
The Lieutenant did not move from the one-way mirror. "Anatoliy Volkov, amateur painter. Death due to trauma from possession. We had to scrape his brain off the elevator's walls, but forensics say the mental image stayed clear. No interference from all those empty office floors."
The Assistant grimaced. "They never confess anyway."
On the other side of the mirror, a transparent vat was filled with green liquid and body parts. Small tubes and electrodes went to the beeping monitors. The Lieutenant spoke into a mic. "Can you hear me? 'Mendo'?.."
Suddenly, a crackling voice emerged from the speakers.
"Fools," rambled Mendoza from beyond the grave. "I have been shown the truth you cannot face. The Unspeakable--"
She interrupted him. "You mean Hastur."
"You dare!.."
She pressed him again. "Stop it. We're no longer in the nineteen twenties when a double-parked car sent people panicking. Nowadays, teenagers write erotic fanfiction about elder deities buggering each other."
Mendosa fell silent. "You don't understand..."
She continued. "We know about the void outside. We could care less; we've more than filled it. Humankind is so much bigger than the nightmares of a depressed hack from Providence."
A crackle. "I'm dead, am I not?"
The Lieutenant softened her tone. "You are. Now, I need you to tell me exactly what happened."
The Assistant DA dialed a number. "Adam? It's Jack. We got him."
In the crowded hall, a vaguely humanoid shape covered in a yellow cape was standing trial.
"Hastur from Carcosa, you are accused of unlawful materialization and of the possession and murder of cultist Anatoliy Volkov. How do you plead?"
