Crawford Tillinghast was killed when a machine that he built in order to break down the barriers between dimensions exploded, and his three domestic servants disappeared, leaving his old friend David Dearden as the only witness to the catastrophe. Now Dearden has to return to the house where the unexplained tragedy occurred. in order to help Tillinghast's widow put the estate in order. Three scholars with whom Tillinghast had been in correspondence regarding his research are also there, avid to get their hands on the remains of the machine and any documents the scientists might have left behind. The accounts they give of their correspondence with the scientist allow Dearden to form a clearer picture of what might have happened on the fatal night -- but in the meantime, he begins to realize that the phenomenon might yet be repeated, with fatal consequences not merely for the inhabitants of the house, but for the entire region of the north-eastern United States -- and perhaps the world -- unless he can find a way to stop it.