The Three Impostors by Arthur Machen, The Everyman Library edition.

Far more of a challenge than your typical novel, this is the story of three men too absorbed by their own literary interests to realise the truth, or otherwise, of the events unfolding around them. These are Dyson, in thrall to his own imagination, Phillipps, an adherent to science, and Russell, who simply considers himself a realist.
  Structurally based upon R. L. Stevenson’s ‘New Arabian Nights,’ thirteen chapters here act as anecdotal short stories, delivered to Dyson and Phillipps by supporting characters inveigling upon them their recent plights, and on whom we – and they – must trail to decide upon the truth of their motive and intent. If this sounds dry, it is only because to describe it effectively at all on one reading is in itself a challenge.
It’s necessary to place the work in the context of its time.
  First published in 1895, this era of supposed ‘decadence’ amongst the monied classes incrementally seeps through our consciousness. For though only sketched, Dyson, Phillipps and Russell still evoke the lazy wit, diffidence and nonchalance of stoned Sixties rock stars. They seem to live for kicks, their own amusement, and little else. They appear bored, dissolute and need adventure. Only, there is the growing, unnerving feeling in this reader that Dyson in particular cares only for the sating of this need over and above the fate of those who may require his help. Machen doesn’t force us to believe this; he simply plays it out. Such progress through the dark makes the work – if not entirely successful – the page-turner it needs to be.
  So, what’s interesting is what author Machen himself thinks of their status. Is he contemptuous of the three? - not obviously. Does he approve of their self-absorption? - it is never made clear. (As literary impostors, who are they pretending to be?) A clue might lay in the work he released in its wake. The novel ‘The Hill of Dreams’ (1897) may be the longest suicide note in history, in its part-autobiographical depiction of a failing writer whose talent and unique personal vision is overlooked to the point where madness fatally perverts whatever it was he’d earlier harboured. Here, the author seems to be predicting his own fate; what may – and may yet – happen to him if he listens to all those who think he should give up his art and get a ‘proper job.’
  Oh, how we can relate to it…
This was also, remember, the time of Chesterton’s sledgehammer metaphors in ‘The Man Who Was Thursday’ and ‘The Club of Queer Trades,’ and Belloc’s satirical sketches. So, it is possible Machen - to a certain extent – is satirising himself and his generation in the former book.
  Two anecdotal ‘stories’ in particular have co-existed in neat isolation from the rest of ‘The Three Impostors’ for at least the last seventy years. Both ‘The Novel of the Black Seal’ and ‘The Novel of the White Powder’ episodes have rightly made countless horror anthologies through the 20^{th Century and done so again in the imminent, and welcome, Penguin Classics reissue, ‘The White People & Other Weird Stories.’ With their contemporary themes of archaeological intrusion and unchallenged drug addiction resonating down the decades, Lovecraft, Howard and their offspring have been milking those particular seams ever since.}