"Recognition"

by Brian Lumley

originally published Weirdbook 1981

Lord David Marriot has gathered a group of psychics and scientist to rid his recently acquired property, "a large, ungainly, mongrel architecture of dim and doubtful origins", of its ghosts.  Or whatever.  Two mediums are to define the entity, and a priest is to exorcise it.

It seems the house has an unsavory rep, including the finding of some pagan worship, involving a spider-like god, and some connection to the De La Poers, of ""Rats in the Walls" fame.

A seance is held, which ends with medium Jason Lavery shouting "Atlach-Nacha" and being tossed about the room.  This leads to Lanford, the priest, bailing.  As does Lavery.  Meaning the only one left is Turnbull, the other medium.  He demands to be left alone in the house while he attempts to do his psychic thing.

This turns out to be a bad plan.  In the morning, Turnbull is found dead, covered in strange wounds.  On his sketchpad is a drawing of, presumably, the house's supernatural occupant - a spidery monster.

Very pulpy but fun tale from The Lum.