It is a curious kind of question to ask, but what kind of a book is Stella Maris? In a daring move, the publishers brought out Cormac McCarthy’s new novel The Passenger last month, and then this other new work this month. I have known of novels – often science fiction – which are scheduled at six month intervals. But this is unique, particularly because McCarthy is such a renowned figure. So what is this book?

It is not a sequel to The Passenger. It is not a parallel text, telling the same events from a different perspective. It is not really part of a literary diptych, as it is stylistically very different indeed – it would be like having a diptych with one half from the Baroque period and the other half in startling Cubism. Is it, perhaps, a pendant to the first novel; or a ravelling up of unanswered question? Not really. The publishers have opted for “coda” which seems as good a word as any. I suppose I would describe the relationship between Stella Maris and The Passenger as akin to symbiotic. Now, having read Stella Maris, I went back and looked over passages of The Passenger, and they appeared in a different light, like changing the angle of a mirror. Likewise, The Passenger sets up some of the mythology which Stella Maris expands.

It is, whatever it is, quite remarkable. As with only a few other authors – Roberto Bolano, Brian Catling – it has the distinction of having given me bad dreams. Scratch that: nightmares. I mean that as a compliment. The Passenger introduced Western, a marine salvage diver who turns fugitive. We learned that his father worked on the Manhattan Project, that his mother died when he was young, and that his sister, Alicia, is both a genius and insane. There were also dark hints from Western’s roguish friends that he was in love with his sister. Western is not just a fugitive from nefarious forces with inexplicable agendas, but a fugitive from his own past. In Stella Maris we get Alicia’s full-on flight from reality itself.

Cormac McCarthy PIC: Mark Von Holden/Getty Images

“Stella Maris” is a “non-denominational facility and hospice for the care of psychiatric medical patients”. A note, dated October 1972, reports that Case 72-118 (is that a nod to how many patients were admitted that year?) is 20, Jewish/Caucasian, female, arrived with $40,000, is a doctoral student in mathematics, has been diagnosed with paranoid schizophrenia and has been a resident on two previous occasions. At least one of my hunches from reviewing The Passenger proved to be right. She is not, we find out, actually called Alicia, but changed her name by deed poll using forged documents from Alice.

Alicia, to use her chosen name, is caustic, wry, rebarbative, sarcastic and dismissive. She is also phenomenally clever, and the book takes in topology, physics, ethics, Schopenhauer, Grothendieck, religion, music and at times wonders if mathematics is something we impose on the universe or a set of truths that would exist without any consciousness to comprehend them. She has a pleasing disregard for Carl Jung. It is pretty heady stuff, and one can see that McCarthy has made good use of his time at the Santa Fe Institute for multidisciplinary research. Alicia revels in being a paradox – that she was sane enough to know she had to go to an insane asylum. She certainly does not go easy on her psychiatrist. (A slightly indulgent anecdote: when I had had my insides visiting the outside world, I developed delirium from the painkillers, so a psych was sent. My Dad arrived and the ward sister told him I was seeing the psych and he said “Poor sod”. She replied, “No, he’s in very good hands”. Dad said, “I wasn’t speaking about Stuart.”) It is not so much that this Alice has fallen down a rabbit hole, she excavated the rabbit hole with her fingernails and built a labyrinth at the bottom for good measure.

Formally, the book is only the interchanges between Alicia and Dr Cohen (with the exception of the fake document about Stella Maris on the first page). The reader has to be nimble in not skipping, although the longer disquisitions are usually Alicia. This form is reminiscent of the Greek stichomythia, to use a technical term, which in tragedies in particular uses alternating lines of dialogue to emphasise the underlying conflicts. One of the few books I know in a similar form is William Gaddis’s equally difficult JR. So, from the very first page, we get: “How are you? Are you all right?” “Am I all right.” “Yes.” “I’m in the looney bin”. She is a master of negation: “I’m not really serious”. “Oh”. “Alicia’s okay. I prefer it to Henrietta”. “You’re not being serious again”. “No”.

Alicia’s one condition is that they do not speak about her brother, which they duly do. She tells us about her hallucinations – the Thalidomide Kid and his vaudeville entourage from The Passenger – and her self-awareness about them, which includes using maths to figure out their heights and being sceptical about them having any meaning whatsoever. In some ways the reference to Greek tragedy is key. Western and Alicia are a modern day Orestes and Elektra, siblings from a cursed family, fleeing Furies. The two together, for two doomed not to be together, are a staggering achievement.

Stella Maris, by Cormac McCarthy, Picador, £20

Book review: Stella Maris, by Cormac McCarthy