An Exorcism, by J.P. Bowie

 I've only ever written one story that involved a serious haunting with ghosts and malignant spirits. Aptly titled A Ghost Story: The excerpt's a bit long, and draws heavily on just about every Hammer horror film I ever saw.

Robert ‘Robbie' Clavell, a young Victorian poet, is murdered by George Russell, a jealous competitor who also invokes an ancient curse that forces Robbie's spirit to remain earthbound.
When Jamie Barrett receives a phone call from his mother telling him of strange knocking noises and furniture moving about, he travels home to  give support to his mother and his twelve year old niece, Laura.
A psychic, Kevin Singleton, explains to Jamie and his mother that their recent family tragedies had opened a portal allowing base spirits to enter and feed off of Laura's youthful and vibrant energy.
 Kevin tries to exorcise Russell's spirit, but  an even darker force is summoned - one that could not only destroy the house and everyone in it, but ensure Robbie's spirit will never find his way home.
 ***
Kevin didn’t like what he was about to do but felt strongly it was the right thing. Slipping from the bed he shared with Jamie, he quickly pulled on his jeans, a T-shirt and a pair of trainers. Quietly, he left the bedroom, satisfied by the sound of Jamie’s steady breathing that his departure was undetected. He found Jamie’s house keys on the kitchen table, pocketed them, then picked up his car keys and exited the flat, closing the door softly behind him.
The rain-slicked streets were dark and deserted as he drove the relatively short distance to Walm Lane. It gave him time to reflect on what he was doing and the knowledge that Jamie would no doubt be pissed at him for going it alone, but as eager as the young man was to help him, Kevin’s intuition told him it was best Jamie not be there when he confronted George Russell’s spirit—and whatever was aiding and abetting him—if there was indeed a second malignant spirit there. He could only hope that somehow the combination of Robbie’s strength and his own psychic abilities might just be enough to oust Russell from the house. He wished there had been something in all that research to help him, to give him direction, but whatever—his own experiences, and hopefully Robbie’s help, were going to have to be enough.
Parking his car outside the house, he pulled a flashlight from the dash then glanced up at the darkened bedroom windows. A shiver ran up and down his spine, and before he opened the front door, he sent out a gentle mind probe searching for Robbie’s presence, but nothing came to him. Straightening his shoulders, he turned the key in the lock and pushed the door open, stepping quickly inside.
He could almost feel the silence, it was so ominous, so insidious, and it seemed to fill every corner of the house with a sinister stealth. Taking a deep breath, he walked towards the stairs, each step creaking under his feet as if to add to the atmosphere of creepiness that pervaded the house. Beads of sweat prickled at his eyelids, his hand felt clammy on the banister and a trickle of sweat ran down his spine. A faint stench of decay, sickeningly sweet, permeated the air.
“Jesus,” he muttered.
He had never experienced anything this menacing before. For the first time since he had begun using his psychic powers, he was afraid that what ability he possessed would not be enough, that maybe he had been foolish to attempt this alone. Perhaps waiting for Lisa to return from London was a better idea. But it was too late now.
His flashlight picked out the darkened landing ahead and the still-closed doors to each bedroom. He almost jumped out of his skin when all three doors suddenly swung open, each one banging loudly against the bedroom walls in quick succession.
“Fuck!”
All right, just a show of strength, made to shake me up a little…well, maybe more than a little.
He trained the flashlight on the open doorway to Laura’s room. Shadows moved and twisted in the beam as if caught in some spectral struggle. He saw a blur of white amid the darkness—Robbie’s shirt? He inched his way towards the door, which was suddenly slammed in his face. He jumped back as it was just as quickly flung open again.
Now he could clearly see what was happening inside the room, and his mind was momentarily frozen with horror at the sight. George Russell’s spectre was locked in combat with Robbie, their hands around each other’s throats. But what was even more terrible was the huge dark shape that hovered over them, a shifting miasmic mass that emanated pure evil. Black tentacles floated Black tentacles floated over Robbie’s head, then dipped down, encircling his body, adding their weight to what must be the already crushing power of Russell’s stranglehold.
Behind him, Kevin heard a door slam and the sound of feet thundering up the stairs.
No!
“Jamie, what the bloody hell? How did you get here?”
“Took a taxi. We’ll have a row about this later.” Jamie gave him a glance that was both a smile and a glare, then his eyes widened in shock as he took in the scene in Laura’s bedroom.
“Bloody hell,” he breathed.
“Now you know why I didn’t want you in on this,” Kevin said between gritted teeth.
“Safety in numbers,” Jamie muttered, gripping Kevin’s arm. “What do we do?”
“Wait. This could go on for hours.”
“What?”
“This isn’t an earthly struggle, nor even a human one. This is a struggle between good and evil in its rawest form.”
“But what’s that bloody awful ugly thing in the middle?”
“I think that’s whatever Russell summoned up through black magic.”
“They don’t seem to know we’re here.”
“Robbie knows. He opened the bedroom doors. He’s blocking our presence from Russell, and that thing. He needs my help…”
“Our help.”
“Jamie, you have to stay out of this. It could get very nasty, and I don’t want to put you in any danger—”
“Too late!”
Kevin felt a weakening in Robbie’s strength and his mind was hit by a powerful surge from the black shape that now swooped down towards them. Both Both he and Jamie were knocked backwards, Jamie landing near the edge of the stairs and slipping down the first few steps. Kevin reached for him but felt himself being lifted off the ground and dragged into the bedroom, suspended over the still struggling forms of Robbie and George Russell.
Distantly he could hear Jamie call his name, voice sharp with fear, but his mind was invaded with a jumble of raucous sounds, a disturbing loud whining noise he couldn’t shut out of his brain, then a fearful pain that shot through his entire nervous system, rendering him incapable of movement. He was only vaguely aware of falling before his body hit the floor with a bone-jarring crunch.
“Jesus, Kevin…”
Hands cupped his face, then tugged at his shoulders trying to get him into a sitting position. He groaned at the effort it took for him to comply, then he was on his knees, staring up at the black shape that pulsated and twisted over him. A breathy gust of corruption emanated from it, passing over them like something foul and noisome.
“Jamie, get out of here,” he rasped.
“I’m not leaving you, not with this smelly…thing!” Jamie looked up at the roiling mass. “Fuck off!” he yelled. “You have no business in my home—get the fuck out!”
The shape grew larger, denser, and a low rumbling sound poured out of it. It was forming words, ancient words that grated on their ears. Despite the pain that still coursed through Kevin’s body, he struggled to his feet. He understood this language! How, he didn’t know, but the words that reached him were clear and intelligible. The black shape seemed to ease itself between Robbie and Russell, ending their brawling, at least for the moment.
“Berantha acroto labhair… I am summoned against my will,” the entity ground out, “but I must fulfill what is necessary…”
“Ciod e ud?” Kevin challenged it. “What is necessary?”
“The destruction of Robert Clavell. His spirit must not prevail. He must be sent into everlasting oblivion.”
“But why?” Kevin demanded. “What Russell demands of you contravenes the laws of nature. He is a murderer. His motives are jealousy and hatred, and—”
 Kevin was suddenly knocked off his feet, the form of George Russell’s spirit on top of him. Jamie cried out in alarm and tried to pull Russell away from Kevin’s struggling body, but the fabric that was Russell’s coat dissolved into clammy nothingness at his touch.

“Robbie!” Jamie yelled. “Do something!”
But even as Jamie watched, Robbie’s once-vibrant appearance seemed to fade and be absorbed by the dark entity that began to fill the room.
It was Kevin himself who stopped Russell in his tracks. Muttering something under his breath, he swung a fist at Russell’s head and Jamie yelped as he heard the sound of the punch and saw it connect with Russell’s temple. The spirit howled and fell over onto its side, then bounded upright, its pale face fixed with a baleful expression as it glared at Kevin, anger tinged with something that looked close to fear.
Jamie had no time to ask how Kevin had managed to physically connect with Russell’s ghost, for now Kevin was facing the spirits down, challenging them in the language the dark entity had used.
“I have read your minds!” he shouted, taking a step towards Russell and the shifting black mass. “I know how the curse works—and now I will reverse it!”
From his mouth poured a torrent of strange, barbaric words. The swirling miasma seemed to rear back as if in shock, its twisting movements becoming less menacing, its darkness losing its density, appearing almost translucent.
“What’s happening?” Jamie whispered, gripping Kevin by the arm.
“That’s it, Jamie,” Kevin said, his jaw clenched hard. “Give me your strength. Let’s send these bastards to Hell, where they belong!”
George Russell’s spirit screeched with rage, the sound as grating as stone on glass, but as Kevin’s voice got stronger, louder, and the incantation continued to weaken the malignant entity, Russell began to cower under Kevin’s tirade, while Robbie’s spectral form became brighter, gaining power from Kevin’s verbal attack. Robbie moved to stand by Kevin, and to Jamie’s amazement he took Kevin’s hand. Jamie could feel the surge of power course through Kevin’s body. His own hand tingled where he gripped Kevin’s arm, and before he could stop himself he yelled, “Yes, you bastards! Get out of here!”
The air around grew deathly cold and the walls seemed to bow in and out, the floor beneath them undulating, causing them to stagger. Kevin held tight to Jamie, pulling him into his arms as the entire room and everything in it shook and shuddered. Jamie held on to Kevin with all his might for fear he’d be torn from his grasp. Then another amazement as Robbie wrapped his arms around them both, protecting them from everything that was being thrown at them.
A horrendous scream tore at Jamie’s senses, searing its way into his brain, and he cried out, watching with horror as George Russell’s spirit was pulled into the midst of the swirling mass he had himself summoned to help destroy Robbie. Now it lifted him off the ground and held him aloft before sucking him into what Jamie could swear was its mouth. A huge, dark, slathering mouth—something he never wanted to see the likes of again.