This novel first came out in 1937, and was written by a man known chiefly today for his extensive novel "A Glastonbury Romance" (clocking it at over 1100 pages) and novels related to Welsh history and settings.
Morwyn is a bit of an anomaly in that, while two thirds (and subsequently half) of the cast is Welsh, the novel takes place, for the most part, in Hell.
The author, reffered to in story only as Captain, though once reffering to himself as Captain Shandy, finds himself accidentally falling into a subtarenean cavern along with a girl he knows is in love with him and her anonymous father, a well known vivisectionist.
Surely the word "vivisection" is said more often in the novel then almost any other. The seeming purpose of this fantastical journey is to condemn the practise of vivisection and equate it to that of religious fanaticism. And in case one doesn't get the message right away, Powys is sure to repeat it, many times. Indeed, the narrator finds the need to repeat the same things over and over again, such as when he and the girl and her father are talking a walk in the beginning of the novel, where the same thing about the girl Morwyn's feelings for the narrator are repeated so often that even the writer himself feels the need to comment on it.
And it's not just that either. The scenes of having a scientific and religious sadist go on and on as to how their torture is justified by religion/science repeat way too often. Part 1 ends with having both the girl's deceased father and Torquemada to provide that contrast, then a random priest and scientist at the end of part one, and then another pair a few pages later in Part 2.
The novel picks up again when the narrator and co. are trying to escape an army of ghosts who want to torture them to death for their own amusement but then sort of just stops and we have scenes where Socrates and the welsh poet Taliesin and basically everyone else go on lengthy sermons as to the evils of vivisection. The novel then ends with Morwyn going on an anti vivisection pilgrimage to America with her father's supposedly repentant ghost while leaving the narrator to be carried home by the ghost of Socrates. She even takes away the main character's dog for "company", but while she is doing all this, abandoning the seriously injured narrator to go on her "holy quest", she never wavers in her actions, despite the fact her father is obviously just faking his supposed reformation, as he bluntly states in front of her to the narrator that he still thinks a little suffering to the "lower animals" and "even lower races" can bring benefit to humanity. And yet she takes no note of this, despite this same man having wagered his own right of parenthood not to save her life, but to instead exchange it for the right to torment the narrator's dog. We never do find out if she ever came back to Wales either.
The novel's biggest problem is that, while it tries to tackle the fantastic, it gets too caught up in how it wants to make absolutely sure to denounce the evils of vivisection on every other page, to even properly describe events the reader would be interested in, like the narrator's return to the surface. It ends up being not bad but rather flawed and far less interesting then it could be, not really fullfillng the promise of being "a terrifying journey into Hell" as the Dennis Wheatley Library of Ocult cover blurb states.