Uninvited visitor

Albrecht hastened to answer the insistent pounding on his door. He opened the door and looked out. The stranger was tall and handsome, dressed in a strange grey suit that covered his entire body. On his back was a wooden box with hoses and cables and levers sticking out of it, and a large, thick hosepipe terminating in a flared metal tube polished to a bright shine.

Albrecht opened his mouth to say something but the stranger beat him to it.
"Good afternoon sir. My name is Felix Welcher, exorcist extroadinaire. I hear you have a little, shall we say uninvited guest?" Welcher stuck out a gloved hand. Albrecht took it, too stunned to think of anything else to do.
"Well? Speak up, man!" insisted Welcher. Albrecht nodded and led the way, open-mouthed, around the back of the house.

The old shed was shabby and run-down. Several boards were missing from the walls, and the door was sagging on one hinge. Welcher looked the place up and down, and strode determinedly forwards.
"Looks like a routine job," he muttered to himself, unslinging the box and placing it gently on the ground. He reached the doorway and peered in. The inside of the shed was no better than the outside. It was covered in a thick layer of dust which obscured the faint outlines that could be made out in the intermittent sunlight streaming in through the holes in the walls. The air inside had a murky feel. Welcher stuck out his tongue, then chewed thoughtfully.
"Yep," he said, "it's in there all right. I can taste it." Just then his world exploded in blue light, and an unseen force knocked him backwards. When his vision cleared, he looked up to see a blue spectre floating a few yards above the shed roof. It was transparent, and looked disturbingly human. The spectre peered at Welcher and moaned in a low voice.
"The box!" it screamed. "The box!" Albrecht could almost swear that there was unreasoning terror in its voice, and guessed that whatever the box was, it must be good at killing ghosts.
"Nooooooo!" the spirit screamed again, and disappeared in a flash of blue light.
"One of those ones, eh?" muttered Welcher, smiling to himself in some unfathomable state of amusement. He stood up and retrieved his box.
"What exactly does this box do?" asked Albrecht. Welcher looked down upon the farmer as a scholar would do to a simpleton, with a "Don't you know? Everybody knows what this is" expression plastered across his face.
"It destroys the ghost," he replied simply.
"How?"
Welcher sighed. "Magic," he said. "I used to be a cleric, you know. It sends out a pulse of negatively charged psychic particles, thus disrupting the flow of the spirit's energy." Albrecht nodded sagely, not understanding anything after the part about being Welcher being a cleric.

Welcher hoisted his box, pushed a few levers, turned a few knobs, rattled a few pipes. A strange hum began to emerge from the box's inner workings, and a weird glow began to play about Welcher's gloves where they touched the timbers. Static force made Albrecht's hair stand up straight.
"Stand back," Welcher said. "This could be dangerous."
Albrecht obligingly retreated to the corner of the house.
"OK, ghost. Here I come." And with that, Welcher hoisted the metal tube in his hands and kicked the door off its hinge. The blue glow saturated the inside of the shed now, and Welcher slowly advanced inside.
"Nooooooo!" came the wailing, from Welcher's left. He spun and dropped to his knee, depressing a lever set into the side of the tube. The humming from the box grew to an incessant scream, and a stream of hazy blue light vomited forth from the tube, striking the ghost and enveloping it. The spectre moaned in tormented agony as it fragmented and dissipated.

Then the box exploded.

From his vantage point, Albrecht watched the rotted timbers fly out from the shed as tongues of blue fire poked out through the walls and licked at the wood and surrounding grass. A particularly large chunk of wood flew past his head and smashed into the wall of his house, and he turned and fled.

Welcher moaned and clutched his aching head. Slowly he checked himself to make sure nothing was damaged. Apart from the headache, nothing seemed amiss. He slowly sat up and waited until the pounding in his head had receded to a dull throb. There could be no doubt about it, that was one obliterated ghost. Then he heard a noise outside the shed.
"Yep, it's in there all right," came a strangely familiar voice. "I can taste it." Slowly his vision focused on a face poking through the doorway. Recognition suddenly dawned on him, and with it understanding. He screamed in panic, and blue fire exploded from his mouth. He rose up, through the roof, and into the air above the shed.
"The box!" he screamed. "The box! Nooooooo!"