From The Art and Popular Culture Encyclopedia
It recounts the terrifying story of how Theodore Wieland is driven to madness and murder by a malign ventriloquist called Carwin.
Wieland (whose name is a German name for the Devil, see Woland) is master of a landed estate near Philadelphia, which he has inherited from his father, an immigrant from Germany. Wieland Senior was a man of strange inclinations who, having built a temple on a hillock in the grounds, devoted to his own idiosyncratic religion, later dies mysteriously of spontaneous combustion. Wieland inherits his father's god-fearing disposition, as well as his land. However the rural idyll he shares with his wife, children, sister and best friend is shattered when he becomes prey to the trickery of Carwin: a mysterious ventriloquist who has moved to the area after leading an undercover life of deception in Europe. Under the influence of religious mania and Carwin's trickery Wieland kills his wife and children as a demonstration of his obedience to a 'divine voice'. In court he expresses no remorse for his deeds and later escapes from prison to attempt the life of his sister, before being stopped in his tracks by the command of a final 'divine voice', which in reality emanates from Carwin. Wieland then commits suicide.
The story is told as a first person narrative by Wieland's sister Clara. As the story proceeds her initial calm and rational disposition is sorely tried by the uncanny and bloody events of the story, which reduces her, by the end, to a state of near mania. Her relations with the deceiver Carwin are ambiguous, veering between attraction and repulsion as the story unfolds.
Apparently the novel was based on the true story of a multiple murder which took place at Tomhannock, New York (a hamlet near Pittstown) in 1781. Mirroring the incidents of the later novel, one James Yates, under the influence of a religious delusion, killed his wife and four children, then attempted to kill his sister, and expressed no remorse for his conduct in court later.