Trevor spent his early life in Europe but eventually moved to Arizona and sets The Sibling in New England.  Obviously I wish he had set his tale in Britain or France or Spain or even Arizona, so I could feel I was getting legit local color and not just a foreigner's view of the Northeastern US learned from TV, but there it is.  I liked his book about armored warfare even though it seems he served in the RAF and not the British Army, so maybe everything will be OK.

The first scene of The Sibling takes place at the funeral of an eccentric old woman who has an Egyptian prayer (in English translation) read over her dead body and who is buried in her Rolls Royce.  (Nothing about this woman figures in the plot and she is not mentioned after the funeral so I guess Trevor started his novel with this funeral just to foreshadow The Sibling's occult and eternal life themes and make it clear the main characters are rich.)  We meet Lorraine Stuyvesant, 41, and her English friend, Alison Scarborough, 37, a jokey horny widow.  It is the holiday season, and Lorraine's 15-year-old daughter Deborah ("Debby") is coming home from her fancy school in Switzerland soon.  The birthday of Lorraine's 16-year-old son Raphael ("Raff") is just six days before Christmas, and after flirting with his own mother (gross!) Raff dances at his birthday party with Alison, who is sexually attracted to Raff and doesn't keep it a secret.  Debby was supposed to make it to the party, but she is delayed in Paris by snow, and we get the idea that Debby doesn't want to come home and that her relationship with Raff has long been terrible, the subject of much expensive psychiatric attention.  Lorraine inwardly fears this Christmas season is going to be a total disaster, Trevor foreshadowing that the large cast of characters (among them a genius pianist who defected from the Soviet Union, a teen-aged girl--Kim--who has a crush on Raff, and a teen-aged boy--Jerome--who has a crush on Debby) is going to be subjected to a massacre!  (See epigraph above.)  Spoiler alert, Trevor doesn't follow through on this foreshadowing, and Kim and Jerome quickly disappear from the narrative.  I feel like Trevor wrote the first two chapters or so of The Sibling with the idea the novel was going to go places it didn't end up going.

Debby finally arrives and Mom compliments how good her legs look and that sort of thing--Debby in turn wishes she was as sexy as her mother.  This novel has considerable appeal to incest fetishists.  Through flashbacks (for example, Raff tormenting Debby with a snake, and little boy Raff threatened by a berserk horse after Debby locks him in the stables--there are a lot of animals in this novel for some reason) and interior monologues we learn how much Raff and Debby hate each other.  Poor Debby is so scared of Raff that she vomits on the plane and pees her pants when she arrives at the family mansion.  But after three years apart, each of these two mental cases is shocked to see how the other has grown into a sexy teen and Raff and Debby instantly become enamored of each other, embracing so each can  feel the other's heart beating through their chests.

The siblings spend the next few days thick as thieves, playing games, including increasingly extreme versions of hide and seek and tag until they jump into separate cars and chase each other on a curvy road, leading to a crash that injures Debby.  She's OK by the time the Christmas Eve party rolls around, at which Alison comes on to Raff as they dance and then Raff comes on to Debby as he dances with her.  Then there is the bizarre incident at the party when Debby sips her drink and finds somehow she has been given a glass full of human blood!

At first, when Debby realizes her brother is getting erections while they are hugging or dancing, she tries to put an end to their physical intimacy, but is her heart in it?  After all, when she masturbates at night, it is Raff's face that comes unbidden into her mind!  Zoinks!  

Alison seduces Raff, and she expects to be in charge of his sexual awakening, but the boy goes berserk and knocks her out and rapes her, apparently possessed by some other being--even Alison realizes when she looks at him after she has regained consciousness and he has regained his composure that "...he looked like Raff....But he wasn't.  He was somebody else."

The story proceeds (The Sibling is like 290 pages, the rape of Alison occurring around a third of the way through) and while Raff and Debby's sexual desire for each other mounts, voices in Raff's head, apparently those of people from ancient times, like we are reading something out of Weird Tales, keep urging him to kill Debby.  Trevor is a good writer and everyone's dialogue and behavior rings true, and his descriptions of the moonlight and the temperature and the stars and the snowfall don't burden or slow down the narrative, but add to the atmosphere and the vividness of the images as Raff does risky things like walking on thin ice or climbing the mansion's mansard roof and then convinces Debby, who is falling madly in love with her brother, to join him in these life-threatening behaviors.

In the middle third of the novel what is going on with Raff becomes more clear as he has visions of life in a murky past of castles and chariots, seeing through the eyes of a young man who spends a lot of time witnessing a priest perform human sacrifices.  In a somewhat silly scene, the family psychiatrist hypnotizes Raff (without Raff's consent or even knowledge) and works some past life regression therapy on the kid.  The shrink finds that Raff is a reincarnation of Tarkon, some kind of prince (who I guess raped a woman--Raff was animated by the memory of that crime when he raped Alison.)  Tarkon had a sister, Iadris, of whom he was very fond and whom he rescued from an attack by a rabid canine.

While the shrink and Lorraine brainstorm ways to cure Raff, Raff uses adventure fiction tricks (like wearing a white lab coat as a disguise) to infiltrate a local hospital and steal small parts of cadavers.  You see, the priests of Tarkon's people would cut little parts off of their sacrificial victims and toss them to ravens (which is why the cover of the copy of The Sibling I am reading has a picture of a bird on it instead of one of a pretty girl and/or her pretty brother.)  Raff puts the parts in little gift boxes and leaves them in Debby's room.  Debby, though disgusted to the point of vomiting by these offerings, is so in love with her brother that she pretends to like these monstrous gifts and resolves to hide her brother's crimes from the world.  She tosses each gift out the window and a raven snatches them. 

Additional sneak-attack hypnosis sheds light on why Raff, who on the one hand loves his sister, is always putting her in danger.  When a plague started ravaging Tarkon and Iadris's country, the priests told their father that only the sacrifice of Tarkon or Iadris could end the plague.  (I guess these primitive people didn't think of shuttering the schools and restaurants and making everybody wear masks.  Civilization has come a long way!)  The weakest parts of The Sibling are Raff's repetitive and tedious visions/memories of Tarkon being told by his advisors that he had to make sure the priests killed Iadris instead of him.  Tarkon is shown to be a guy with a ferocious temper, always flying off the handle and having to be restrained from physically attacking some advisor.  These cardboard medieval or ancient or fantasy world or whatever figures are pretty boring compared to Trevor's 20th-century cast of people--the sad mother in the distant marriage, her perverted brats, their dutiful servants, the talented defector, the English immigrant who is horny for teenagers, and the shrink who thinks he is on the verge of making a groundbreaking discovery.  I wanted to see what happened to the Connecticut people, but these ancients and their nondescript setting left me cold.  

The final third of the novel begins with Raff killing a friendly dog owned by Kim's family--its appearance triggered Raff into reliving Tarkon's fight with the vicious dog that threatened his sister Iadris so long ago.  Raff's macabre thievery from the hospital escalates (he wants some fresher body parts to offer Debby.)  Lorraine and the shrink, fearing Raff might harm Debby, decide to separate her son and daughter, to send the boy to a madhouse and the girl to her European school.  Debby learns of this plan and in one of the novel's best scenes Debby gives an impassioned speech about how middle-class parents screw up their kids by working too hard and thus neglecting their offspring and then offloading them to shrinks who are all charlatans and instead of curing the kids just make them crazier.  This speech of course totally rings true to me (go Debby!) but at the same time we readers know that the real reason the kids are dangerous bloodthirsty incest-monsters is the reincarnation jazz.  

(I wonder if I might like this novel better if Trevor had concentrated on the bourgeois-parenting-turns-kids-into-killer-perverts angle and jettisoned all the supernatural reincarnation business.)

Raff gives Debby another gift--some poor bastard's penis!  Then he murders a guy, thinking to offer her an entire person, though events prevent Raff from lugging a corpse into the mansion and up the stairs into Debby's room.  (The scene of the murder is good horror stuff, written from the point of view of the victim but focusing on his fear before the attack, not the actual physical fight and the gore.)  The penis is almost a bridge too far for Debby, and she comes close to agreeing with her mom and the shrink that maybe Raff really should be sent to the funny farm, but her faith and love for Raff is strong enough to overcome her temporary flirtation with collaboration with the adult world.  Debby warns Raff about the plan to involuntarily commit him and the incestuous lovers run away from home in the Jaguar that Raff received for Christmas, driving into a ferocious blizzard.  (Wind is a theme of the novel, Tarkon and Iadris's unspecified homeland being very windy.)  

After a pretty well-written car chase (Trevor put out a ton of espionage novels and I'm guessing he wrote lots of car chases) the kids reach a mountain lodge their family owns, where we get the story's somewhat disappointing climax or climaxes.  Raff takes Debby's virginity, what we might call the climax of their relationship.  Obviously this is gross, but it is what we signed up for when we started this book, and the scene is solid.  That is not the disappointing part.

Debby is ready to fight the entire world at the side of her lover and brother, but then she finds out about the murder, that the victim was somebody she knew.  The fact suddenly comes home to her that Raff, all her life, has been putting her in life-threatening situations, as if he has been trying to kill her but just falling short of success.  Now that they are truly alone, separated from the rest of the world by snow covered roads, Debby is scared Raff is finally going to succeed in destroying her, and she takes steps to protect herself.  I expected some kind of showdown, a fight and/or a verbal exchange in which Debby tries to convince her brother to reject the counsels of his advisors, but what we get is one of the siblings getting killed by what amounts to an accident; the circumstances of the accident parallels the methods and practices of human sacrifice among Tarkon and Iadris's people.  As I have told my long-suffering readers many times, I hate deus ex machina endings--one of these horny creeps should have outfought or outwitted the other, surviving thanks to his or her abilities and willpower, and then had to suffer the moral and psychological consequences of killing or imprisoning the sibling they just had mind-blowing sex with.  Trevor's ending robs the survivor of agency and shields him or her from responsibility, which I don't like, even if the whole reincarnation angle implies that people lack agency and responsibility.

I guess I've now read four books mentioned in Hendrix and Errickson's Paperbacks from Hell, and The Sibling is perhaps the best of them.  I say "perhaps" because while I thought Garrett Boatman's Stage Fright and William Schoell's Late at Night were garbage and Trevor here with The Sibling outclasses them by miles, I also enjoyed Peter Tonkin's Killer nine years ago and my memory of that book, about people fighting an orca, is too hazy for me to choose between them.  Still, a definite thumbs up for The Sibling.

As I have suggested, Trevor's style is good, and the sex scenes and action scenes and horror scenes are quite effective.  My fears that Englishman Trevor wouldn't be able to convincingly write about Connecticut proved unfounded--I didn't encounter any major boners.  Not that there weren't a few odd notes.  We get "knickers" once, instead of "underpants," and once "cunny" instead of "pussy."  Four or five times Trevor gives us "bubbies" instead of "boobs" or "tits."  Well, let's say that Raff and Debby were under the linguistic influence of family friend Alison.  Trevor spells Halloween with an apostrophe ("Hallowe'en") which I don't think Americans did in the 1970s, but I can shrug that off.  One jarring moment was when, in referring to the Jaguar, Trevor used "squab" for "seat cushion," which I had never encountered in my entire life.  Maybe we can excuse that because it is a British car?  Another noteworthy oddity is how Deborah thinks "track-suits" are very sexy--track-suits figure in the most memorable sex scene of the book, as well as other scenes.  I was born in 1971, so didn't reach puberty until after the '70s were over, so am unaware if plenty of people in the Me Decade actually did find track-suits sexy, or if this just says something about Debby. 

I've already complained that the scenes set in unspecified ye olde antient tymes are vague and boring, and that the ending is kind of a let down.  I also think there are too many characters, or that too many of the characters don't receive the attention they deserve; in my view, each character should do something that is exciting or materially affects the plot and each should get some kind of resolution at the end, and many of the people in The Sibling do not.  For one thing, I expected more of the cast to be murdered, and was a little disappointed that anybody who actually was murdered was some minor character who was less developed than Alison the slut, the defector pianist (Raff's real father, Lorraine and Charles having a marriage marked by infidelity), and the shrink who believes in reincarnation.  Trevor concocted interesting back stories and motivations for Alison, the pianist, and the shrink, but he doesn't come up with enough stuff for them to do and story arcs for them that are as compelling as those backstories and are satisfying--shouldn't each of these people get killed or perform an heroic deed and/or suffer some permanent psychological scar?  The novel would be more satisfying if the pianist had killed his bastard son Raff or saved somebody from Raff, and if the shrink's career was ruined by his wacky (but accurate!) theories or he had gotten killed because he pursued his theories too boldly.  As for Alison, she should have gotten killed as metaphorical punishment for her depraved pursuit of teen-aged boys or used her body to liberate Raff from his ancient self's baleful influence so that she represented the healing power of the act of physical love--what stand a novel takes, whether it vindicates prudery or celebrates license, is less important than that it demonstrate its stand with power or eloquence.

So, I've got gripes and suggestions.  But The Sibling delivers the icky sex and grue that we look for in this kind of book, and it is actually well written because Trevor is a seasoned professional writer, leading me to strongly suspect The Sibling is one of the best of the Paperbacks from Hell.

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The printing of The Sibling I read, the British 1981 paperback, has some ads in the back all you historians of mass market genre literature might find interesting.  Are "Book Tokens" still a thing?  If not, when did they go out of circulation?  Did any of my readers from the UK or Ireland ever use a Book Token?  And what about this ad for New English Library bestsellers?  Which is the bestselling?  Which have you read?  I've read the Heinleins and started Dune, but that's it, though I've heard of many of those which became films.  Will Errickson has written about The Rats and The Fog, which I am guessing are the closest of the listed books in tone and content to The Sibling.