(Melchizedek Communique, MC060109) Evelyn Waugh (1903 - 1966, image shown), among his many published stories, wrote one at least which fits into the "conspiracy theory" category.

SPOILER WARNING: Details of Waugh's short novel, The Ordeal of Gilbert Pinfold, follow.

Arthur Evelyn St. John Waugh, commonly known as Evelyn Waugh, portrays some sort of psychotic episode in The Ordeal of Gilbert Pinfold. Pinfold, in poor health, books passage on a ship headed to a warmer climate. Onboard the vessel, malicious voices are heard by Pinfold in his cabin. The voices infest Pinfold with insults and horrible notions. Pinfold strives to understand what is behind the phenomena.

Wikipedia describes The Ordeal of Gilbert Pinfold as "a thinly-veiled fictionalisation of Waugh's own real-life experience of alcoholic hallucinosis. This short but disturbing malady was almost certainly caused by alcoholism but Waugh preferred to blame the interaction between alcohol and sleeping medications." [1]

In the Everyman's Library introduction is described how in 1954, "at the age of fifty, Waugh set out on a winter cruise to Ceylon [Sri Lanka]. He was suffering from insomnia and had been taking a cocktail of various narcotics generously laced with whisky." There was "an extended episode of hallucinatory psychosis." [2]

Throughout The Ordeal of Gilbert Pinfold, "one rationale is added to another to create a tottering hypothetical superstructure on the shaky foundations of delusion." [2]

Towards the end of the tale, Pinfold decides he has at last figured out what has been happening:

Someone from the British Broadcasting Corporation (BBC) and his team is aboard the ship. They carry with them a "new and experimental" apparatus "able to speak and to hear." Pinfold has been spending days and nights speaking with people he does not see. "They are trying to psycho-analyse me. I know this sounds absurd. The Germans at the end of the war were developing this Box for the examination of prisoners. The Russians have perfected it." Pinfold decides he is being persecuted by an unfriendly "conceited ass" from the BBC. [3]

Later, Pinfold learns that the persecuting BBC reporter has been in England all the time Pinfold was on the ship. "They must be working the whole thing from a studio in England," decides Pinfold.

Then, from his doctor, Pinfold discovers that the voices had been caused by prescribed pills mixed with un-prescribed bromide and chloral. It has all been "a perfectly simple case of poisoning."

Yet The Ordeal of Gilbert Pinfold contains the hint of yet another explanation. Pinfold finally knew "that he had endured a great ordeal and, unaided, had emerged the victor." A spiritual combat of some type is discerned.

------- Sources -------
[1] "Evelyn Waugh", Wikipedia, May 31, 2009
[2] From Introduction, by Ann Pasternak Slater, to Everyman's Library (#265), collection of four Evelyn Waugh short novels,
 including The Ordeal of Gilbert Pinfold. New York: Alfred A. Knopf, 2003
[3] The Ordeal of Gilbert Pinfold, by Evelyn Waugh. New York: Alfred A. Knopf, 2003