People who knew Yeats personally, especially in his younger years- were inclined to find him rather silly- and a story like Rosa Alchemica- heavy on the esoteric showing off, light on characterisation and plausibility- is- as it were- evidence for the prosecution. The protagonist is a wealthy and reclusive aesthete- of the kind common in fiction of the 1890s- who lives in Dublin. The Rosicrucian Michael Robartes turns up on his doorstep and uses the fluence to recruit him for his magical order- because that, of course, is how occultists operate. They take a train to the West Coast where Robartes owns a temple at the end of a pier. That night- while Robartes and his guests dance mystical dances- the local,fisherfolk storm the temple like extras from a Frankenstein movie- and our narrator barely escapes with his life. Seeing who has the bigger guns, he renounces occultism and becomes a Catholic.
It's the sort of thing Algernon Blackwood (like Yeats an initiate of the Golden Dawn) might have written- only Blackwood would have done it better.