A story about an Icelandic medium. The word "control", which is used regularly in the story below, refers to a spirit that protects the medium and keeps undeveloped entities from coming through during the trance state. Another way to think of it is the medium's spirit guide. Anyway, in this story it would appear the spirit of a recent suicide gained control and used the medium to wreck havoc.
http://dailygrail.com/Essays/2012/10/The-Uninvited
But in September 1907, one event seems to have precipitated a dark and frightening change in the mediumship of Indridi Indridason. While visiting a village on an island off the southern coast of Iceland, he reported seeing the apparition of a man, one Jon Einarsson, who had drowned himself a year earlier. Upon returning to Reykjavik, strange disturbances started occurring in the rooms which Indridason shared with theology student Thordur Oddgeirsson, and at subsequent séances. The medium also reported that he was having continued visions of the same man he had seen on the island.
Then, during a séance on December 7th, the controls reported to the group that “Jon” was now in attendance, and was in control of “the power”, and in a very bad mood. Indridason went into convulsions, sitters felt their clothing and hats being grabbed at, and a full coal-scuttle was thrown, barely missing one of the sitters. Later that night, when Indridason and Oddgeirsson went to bed, a plate flew from the front room into the bedroom, and the medium’s bed was pulled suddenly out from the wall. Indridason was reportedly terrified by this development – regular sittings were canceled for some time, and members of the Experimental Society had to stay with him at night to calm his nerves.
The following night, Kvaran stayed to reassure the terror-stricken medium, locking the doors to the building and staying in the bedroom with him and the theology student after the lights were put out. Suddenly, Indridason fell into a trance, and his chief control told Kvaran that “Jon” had just gone to get power, and this was very serious. The medium woke from his trance, but then things began to happen:
"The ends of the bed in which the medium and Mr. Oddgeirsson were lying were raised and lowered alternately and the bed shaken. The medium was lying on the side farther from the wall. He shouted that he was being dragged out of the bed, and was very terror-stricken. He implored Mr. Oddgeirsson to hold onto his hand. Mr. Oddgeirsson took his hand, pulling with all his might, but could not hold him. The medium was lifted above the end of the bed against which his head had been lying, and was pulled down onto the floor, sustaining some injuries to his back from the bedstead. At the same moment a pair of boots, which had been under Mr. Oddgeirsson’s bed, were thrown at the lamp, breaking both the glass and the shade."
Indridason was then dragged headfirst out the door of the bedroom and into the front room, despite desperately trying to grab hold of pieces of furniture, and having both Kvaran and Oddgeirsson pulling at his legs. They finally managed to get him back to his bed with great difficulty, but his legs were then lifted so forcefully that the two men could not push them back down to the bed.
Their reaction to these events was a natural one: they got out of the house as fast as possible, went to Kvaran’s home, and turned on all the lights! Nevertheless, phenomena continued – a book flew off a table and hit a hanging lamp in the drawing room, then continued on and hit another smaller lamp; a pot plant shifted a few inches; and knocks were heard on the walls of the room.
The poltergeist phenomena continued on subsequent nights, to varying degrees. On December 10th, the Experimental Society’s harmonium player (and also organist at Reykjavik Cathedral) Brynjolfur Thorlaksson stayed with Indridason and Oddgeirsson, sleeping on a couch in the front room. Indridason once again fell into a trance, and the controls warned that “Jon” had gathered “considerable” power during the day. Two candlesticks were flung to the floor, and a brush was thrown across the room. Indridason then began screaming that “Jon” was there. Thorlaksson went to the bedroom and lay on top of Indridason, and had to use all his strength to hold him down. Oddgeirsson went to his aid, but a bedside table was smashed over his shoulders – he jumped back into his bed and pulled the quilt over his head, but the table continued to bash him mercilessly.
The accosted trio managed to light a lamp and began planning their escape from the building. Indridason started to get dressed, and was putting on his trousers when he was flung down onto the bed again. Thorlaksson rushed to help when a bowl flew from a chest of drawers in the bedroom straight for him. He dodged the missile, but reported that after it passed him the bowl changed direction and smashed into a stove in the outer room. Continuing on into the bedroom to assist the frightened medium, Thorlaksson was gob-smacked by what he witnessed:
"A vision that I shall never forget. Indridi is lying horizontal in the air, at about the height of my chest, and swaying there to and fro, with his feet pointing towards the window, and it seems to me that the invisible power that is holding him in the air is trying to swing him out of the window. I don’t hesitate a moment, but grab around the medium where he is swinging in the air, and push him down onto the bed and hold him there. But then I notice that both of us are being lifted up. I scream to Thordur Oddgeirsson and ask him to come help."
Upon hearing the call for help, the theology student made for the bedroom, only to have a chair hurled at him by some invisible force. Side-stepping the hostile furniture, he continued to the bedroom where he saw Thorlaksson lying on the chest of the medium, whose whole body was in motion. He spread his weight across Indridason’s knees to assist, when the two candlesticks from the front room drifted into the room and were flung onto the floor beside them.
The three men linked arms and began backing out of the room, with Oddgeirsson holding the lamp before them to illuminate any further threats. A hand-basin flew towards them from a table in the bedroom at head-height, then changed direction and smashed into the stove in the outer room, breaking to pieces. At 2.30 a.m., three grown men rushed out of the house into the Icelandic night, terrified.
If the physical violence wasn’t intimation enough that this new presence was a dangerous one, the threat soon became explicit. On December 17th, while staying at Kvaran’s house, Indridason once again fell into trance. But this time something was different. Through choking sounds, it became clear that the usual controls were not in charge of the medium’s body – instead, “Jon” began mumbling and swearing at those present. He then described Indridason as “a trained instrument which he should like to use at his pleasure”, expressing his desire “to kill him and to do all possible harm to those in the so-called upper world”. This seems to have spurred the other controls to combine forces and expel “Jon” from the medium’s body, and diminish his influence. Curiously, as the malevolent spirit was being exorcised, sitters described hearing a buzzing sound surrounding Indridason. But the effort seems to have been a successful one, as Jon’s power seemed to weaken from this point – so much so that he eventually appears to have reconciled and made peace with the medium and the experimental group.