Sins of the Flesh opens with a prologue which takes place approximately thirty years in the past. 19 year old Lizabeth Carstairs, sometime after the mysterious disappearance of her considerably older "husband", Reverend Carstairs, discovered her two dissimilar looking 13 year old sons, Cal and Petey, together in the attic, naked. In an apparently mad state, shouting phrases from Leviticus, Lizabeth murders the two boys with a shotgun.
The reader is introduced to Alan Carver as he is taking a shower. He is an attractive man of about 30 and a moderately successful writer. Alan is, however, tired of living in the city, dealing with his neighbours, and with the help of his literary agent and best friend, Morgan "Morg" Cantrell, he puts a down payment on a Victorian house in the country. With the assistance of his friend and the woman he loves, Annie Raymond, Alan moves into his new home, a place called by the residents of the nearby town Carstairs House.
Alan is a stable man with a healthy sense of humour. He enjoys his friendship with Morgan and his sensual relationship with Annie, a beautiful, charming woman who is not the airhead some people instantly assume she is. However, Alan, drawn to Carstairs House, gradually undergoes a certain subtle change in his psyche. It troubles him, yet he has the stability and humour, the freedom from the Puritanical moral sense that inhibits most people, to deal with the problem. Likewise, although unsettled, he is capable of dealing with the subtle abnormalities he discovers in Carstairs House.
It is during his visit to the local small town of Crowley's Corner that Alan, along with Morgan and Annie, meets the proprietor of Dolly's restaurant and her waitress, Margie. More importantly, Alan encounters Cartwright Merriweather, the owner of Merriweather Curios, a curious little antique store which boasts of a fine collection of antiques, oddities and "antediluvinalia". Merriweather is a charming man in his 40's who, little by little, proves to have a more than passing interest in the esoteric side of nature. He is not exactly what he seems to be and he is far more aware of everything going on around him than anyone can imagine, only in part, of course, because he occasionally consults the tarot. He is, for instance, immediately aware of Alan's inmost nature and his hidden relation to the writer.
While Alan gradually undergoes a certain change in his psyche, experiencing dreams of a pleasant mythological nature, encountering Pan, the ancient Greek goat foot god of lust, another, slightly younger man is experiencing his own dreams and hallucinations. Christopher Andrews is not so unfettered as Alan. As we gradually discover, he was a seminary student on his way to becoming a Roman Catholic priest. Christopher's greatest difficulty in life is his inability to reconcile his undeniable homosexuality with the Church's stand on the issue. He is plagued by obscene fantasies involving both Satan and the crucified Christ, but when it is discovered that he and another student, Jerome, enjoyed a night of bliss under the stars on the seminary grounds, his time there comes to an end. Jerome voluntarily leaves, which saddens Christopher as he considered the young man to be truly saintly, thus increasing his sense of shame and guilt. Father Kevin Michaels, an instructor at the seminary and a father figure to Christopher, seems at first sympathetic when he informs Chris that he may remain, but proves to be rather less understanding as their conversation continues. Christopher decides to leave and go out into the world to look for a solution to his problem. (All of this we learn by way of flashbacks during the course of the story.) Chris is drawn to the town of Crowley's Corner.
It is while Alan and his friends are in Merriweather Curios that the writer meets both Christopher and the town bully, a Neanderthal troglodyte everyone calls Mister Cakkes. (One never calls him by his Christian name, Clarence!) Defending the more sensitive young man, Chris, Alan humiliates Mr. Cakkes, the entire incident witnessed by many of the town's folk. One person especially finds the meeting of Christopher and Alan quite disturbing.
Morgan returns to the city to visit Alan later. Annie stays on a while, and they enjoy their romantic and sexual relationship to the fullest. There is, however, a disturbing event. Their love play becomes a little rough and when they are finished Alan feels as if he had just raped the woman he loves. Annie, with all the love of a woman, accepts it, feeling sorry for Alan as he suffers remorse.
One night Christopher appears on Alan's doorstep, severely beaten by Mr. Cakkes. He is taken in and attended to by the young writer and his lover. Alan and Annie are determined to speak to the local law enforcement officer, but discover that this may not get them very far since Constable Cakkes is the bully's brother.
Annie returns to the city where she is gainfully employed and a later visit is unavoidably cancelled, leaving Alan and Chris plenty of time to get to know one another and further investigate the subtle but odd goings on in the old house. Eventually, by way of Cartwright Merriweather (who, as a young boy, was adopted by the Merriweathers), the story of Carstairs House is revealed. About 30 years earlier the Reverend Carstairs took up residence in the Victorian house a few miles outside of Crowley's Corner. He brought with him his much younger wife and young son, later adopting one of the two young boys orphaned by the death of their remaining parent, a descendent of the town's founder. The two boys, Cal and Petey, were raised as brothers. One day the Reverend simply disappeared and it was assumed he had run off. Later still, Lizabeth Carstairs apparently went mad and murdered the boys. She was judged insane and institutionalized. Following these tragic events, over a period of time, the townspeople managed to put all of the pieces together and discovered that Lizabeth was not really the Reverend's wife. She was his daughter. For years he had molested Lizabeth and when his wife Helen finally protested he murdered her in front of his daughter. After this the Reverend told Lizabeth that she would have to be daddy's wife, that she should never again refer to him as her father, and that she should raise her little brother Peter as her son. It was after this that the Reverend and the remaining members of his family moved to the house outside of Crowley's Corner.
Both Alan and Chris experience dreams and fantasies of a powerful sexual nature, and the attraction between the two men slowly builds. However, Alan feels rescued when Morgan shows up for a visit. Unfortunately for Morgan, his is nearly a fatal visit as the house seems to take exception to his interference. Annie rushes to Carstairs House and it is during this stay that she witnesses something that started earlier and which she never imagined possible. This throws her completely off balance, violently driving the proverbial wedge between Annie and Alan.
Throughout the story we catch glimpses of a woman in torment, a woman who turns out to be Lizabeth Carstairs, judged some years ago to be cured and released to assume a new identity to get a fresh start on life. Unfortuantely, she was herself drawn back to Crowley's Corner where only Merriweather and Constable Cakkes know her true identity, and upon witnessing the meeting of Christopher and Alan things begin to happen. She becomes plagued by nightmarish memories and worse, the dark which she thought banished once again begins speaking to her. He was still with her. Her doctor assured her that he was merely a part of her own personality, but she knows better. It was not she who murdered Cal and Petey. He invaded her body, as he had always invaded her body, and it was him who picked up the double barreled shotgun and blew the two boys to bloody pieces. But he was still there, awake again and in her, and she had to do what he told her to do. She had always done what he wanted. She had to.
Only Cartwright Merriweather saw the whole picture, although even he could not foresee everything, and when Mr. Cakkes and his two knuckle-dragging cohorts, Ernie and Dil, came for him he was ready. Ready for everything but the hunting knife Mr. Cakkes produced, much to his companions' surprise. Cakkes wanted revenge for earlier incidents involving Merriweather that made the brute feel foolish, and he simply wanted him out of the way. That night he planned more than one murder as he too was drawn to Carstairs House. Unbeknownst to Cakkes, Lizabeth was also headed for the house that she had once lived in, controlled by her possessing spirit, the Reverend Carstairs.
To Carstairs House Lizabeth, armed, went to hide in the cellar until the right moment came to "save the souls" of Cal and Petey.
To Carstairs House Mr. Cakkes went that night, also armed, his reluctant henchmen at his side.
In Carstairs House Annie confronts Alan in a heated argument, while Chris checks the furnace in the cellar. And the house is not at all pleased with Annie's attempt to throw something at Alan which could injure him.
Meanwhile, has Mr. Cakkes succeeded in murdering the old mystic, Cartwright Merriweather, or will he be able to make it to Carstairs House in time to help his new friends, save poor Lizabeth, deal with the demonic spirit of the Reverend Carstairs, and save the life of his....?
Must I tell you everything in a synopsis?