In The Cloud of Unknowing, Thomas H. Cook fashions an unusual tale centering on the terrible effects of paranoid schizophrenia. "It's in her blood of course, all this craziness," says Mark Sears, Diana Sears' estranged husband, who unwittingly becomes the primary focus of Diana's campaign to prove that something murderous has happened to her son, Jason.

Jason drowned in the lake behind the family home, but the court recently ruled Jason's death a mishap, a simple "accidental" death. Diana is absolutely devastated at the verdict; she is certain that Mark had something to do with their son's fate, convinced that Mark never really loved Jason

As soon as Jason began displaying the same signs of paranoid schizophrenia as Diana's father, Mark began to see him as damaged goods. He gradually separated himself from his son, disillusioned by the fact that Jason had turned out less than perfect, born with the problem so serious that it had unhinged him, cutting him of from others.

Determined to protect Jason - "for as long as he lives, no one is going to take Jason, and absolutely no one is going to get rid of him" - Diana becomes unhinged after his death. Abruptly she moves out of her house, her life clogged with loss, grief and pain, and she becomes filled with a divisiveness characteristic of the direction that her life will eventually take.

It is left to Diana's brother, Dave, to sort through the riddle of Jason's death as he sits opposite Detective Petrie, recounting his knowledge of the events leading up to Diana's accusations. After a trip to the morgue, Diana accompanies her accusations against Mark with a maze of bizarre associations, her enquiry into Jason's death becoming an almost pseudo-scientific enterprise, a concoction of scraps from anthropology, forensics, mysticism, and even a badge of Mark's.

As her allegations build into a peculiar crusade with bizarre emails and faxes about prehistoric Iron Age murders, labeling them with the word "sinner," she spends her time ensconced in the local library, researching all the weird murders of history.

Abby, Dave's wife, senses that Mark is somehow in danger, but what in actuality is Dave supposed to warn Mark about? Meanwhile, Diana voraciously courts her teenage niece, Patty, seducing her with tales of death and of Mark's possible involvement.

Dave, no longer the passive observer, gradually sees his daughter as a hapless victim of Diana's enigmatic sorcery. Meanwhile, Dave's own world is turned upside down as he is finally forced to confront a mad witch's brew of family secrets and the very real possibility that Diana herself has inherited their father's troubling gene.

Is Diana a seductive manipulator whose frenzied mind is running rampant, seeking to defile Mark's character for no good reason? Or does she have some real proof that Mark was responsible for Jason's death? It suddenly occurs to Dave that perhaps this has been Diana's design all along, to bring her brother back to Jason for a murder she clearly thought no less painfully resolved.

In The Cloud of Unknowing Thomas H. Cook explores the delicate link between madness and intuition. The author sees life through a prism of other possibilities; when we look deeper than the simple, shallow pool in which we swim, we in are fact "left staring bare-eyed into an unfathomable abyss."

The novel works well as a grippingly creepy literary thriller, but The Cloud of Unknowing also works as a provocative study of the cyclical nature of mental illness and the dreadful realization that one woman's life has been plagued with ills and torments that she could not foresee.