Walter Gilman, a student of mathematics and folklore at Miskatonic University, rents an attic room in the "Witch House", a house in Arkham, Massachusetts that is rumored to be cursed. The house once harboured Keziah Mason, an accused witch who disappeared mysteriously from a Salem jail in 1692. Gilman discovers that, for the better part of two centuries, many of the attic's occupants have died prematurely. The dimensions of Gilman's attic room are unusual and seem to conform to a kind of unearthly geometry. Gilman theorizes that the structure can enable travel from one plane or dimension to another.