The Arcanum (2005) by Thomas Wheeler: If there were an award for worst fictional depiction of H.P. Lovecraft, this novel would certainly finish in the Top 5.
At least.
Screenwriter Thomas Wheeler tries for a sort of League of Extraordinary Gentlemen, only with real people and not fictional characters. This team is The Arcanum of the title and in this novel consists of H.P. Lovecraft, Harry Houdini, Arthur Conan Doyle, and Louisiana Voudon 'Queen' Marie Laveau.
Set in 1920's New York, The Arcanum pits our rag-tag group of ghost-busters against a sinister plot that's actually a large-scale version of a standalone, supernatural-themed episode of The X-Files. Many references appear to earlier adventures of The Arcanum, now deprived of its creator as his murder by telepathy starts the events of the novel in motion.
Wheeler depicts Lovecraft as a slightly less cowardly, more magicky version of Ichabod Crane in Tim Burton's Sleepy Hollow. Houdini is a bland cipher. It's hard to make Houdini boring, but Wheeler does it. Conan Doyle gets the most prominent role as the de facto leader of The Arcanum. He may be in his early 60's, but Doyle is totally buckling those swashes against the forces of Evil.
It really doesn't help matters that Wheeler wedges Lovecraft's Great Old Ones into a fairly standard Christian narrative in which the Devil, angels, and Nephilim all appear. Aleister Crowley shows up as a lazily written Crowley, twirling his mustache and leering. OK, he doesn't have a mustache. But he is a one-dimensional jerk.
Perhaps the most unintentionally funny moment comes when Lovecraft wields one of the Eltdown Shards. The shards were created by Richard Searight and used by HPL in his portion of the group-story "The Challenge from Beyond." However, Wheeler, who does not seem to do research all that much, re-imagines the Shards as the fossilized arm of some creature, enhanced by what is basically an Iron Man glove to tap their power. And here I thought they were tablets!
There are probably thousands of better stories featuring HPL, Houdini, and Doyle as characters. Hell, you can just read the story HPL ghost-wrote for Houdini, "Imprisoned with the Pharaohs," aka "Under the Pyramids." You can read about a fictional team-up of Houdini and Conan Doyle in William Hjortsberg's excellent 1996 novel Nevermore. Or you can read The Arcanum and laugh and laugh... Not recommended.
Nevermore (1996) by William Hjortsberg: The 1990's paperback version of Nevermore was clearly designed to resemble the paperback of The Alienist, Caleb Carr's riveting 1990's murder mystery set in New York that combined real people (most notably Teddy Roosevelt and William James) with fictional characters in pursuit of a serial killer. The interior front cover/two-page illustration actually seems to have come from the same photograph as the cover of The Alienist. Hmm.
The resemblance mostly ends there: Hjortsberg does combine fact and fiction, but the mystery and the serial killer are only a part of what the novel explores. As with Hjortsberg's more famous Falling Angel (made into the controversial 1987 movie Angel Heart starring Mickey Rourke and Robert De Niro), Nevermore is invested in mysteries and morality and the oddities of human nature, not in the prime importance of the aims and methods of detection.
Sir Arthur Conan Doyle arrives in 1923 New York to begin his United States lecture tour on the Spirit World and his many attempts to communicate with the dead. Meanwhile, with vaudeville dying, Harry Houdini searches for a new money-making model for his magic shows while also waging a very public war against the mediums and spiritualists whom he views as being dangerous frauds. Despite their radical disagreement on spiritualism, however, Houdini and Doyle were friends.
And a mysterious string of murders, each based on a different work by Edgar Allan Poe, soon seems to be working its way towards either Houdini or Doyle as the final victim.
Hjortsberg does a marvelous job of combining fact and fiction. He deploys a lengthy and detailed set of historical events and personages while keeping the novel light on its feet and often movingly dark and poetic. But Nevermore is also very funny at points. Nevermore's depiction of Houdini and Doyle makes them lively, fascinating individuals. And the sexy spirit medium who has dubbed herself Isis -- what's her game?
Nevermore is more of a novel with a mystery than a mystery novel. Still, it's satisfying in its fictional and factual elements. And you'll find out how a couple of Houdini's famous tricks were accomplished (though not all of the ones depicted in the novel). Hjortsberg even throws in a climax that's wittily movie-like. All this and the morose ghost of Edgar Allan Poe, visible only to Doyle. Highly recommended.

The Psychic Mafia by M. Lamar Keene and Allen Spraggett (1976): M. Lamar Keene was a psychic huckster in the 1960's and 1970's who developed a conscience and decided to reveal the tricks mediums and psychics use to bilk their customers. This book is the result, and it's a fascinating glimpse into a world which, if anything, has grown larger and more fradulent in the nearly 40 years since The Psychic Mafia came out.
Keene calls his former compatriots 'the Psychic Mafia' because there's widespread communication and sharing of information between them, whether they call themselves spiritualists, mediums, or psychics. A medium in Florida may be able to 'read' astonishingly detailed facts about someone 'new' because information has been sent in advance from the medium that person usually sees in Maine. And so on.
This was true long before the Internet. Imagine the ability to instantaneously share information about clients now!
Keene goes into other tricks of the trade, most of them fairly basic sleight-of-hand and mentalist stuff. Chiffon turns out to be the fabric of choice for ectoplasm in a darkened room, for instance, as it looks remarkably smoke-like when the right lighting is used. Other basic mentalist skills such as pick-pocketing, palming, cold reading, and ventriloquism also fill the medium's arsenal.
There's a real sadness to many of the stories Keene tells, as people are defrauded of hundreds or thousands or tens of thousands of dollars by a spiritualist network from which Keene can glean no stories of 'real' psychics...or even people who believe they're real psychics. The entire enterprise seems corrupt, and seems to have been corrupt since the birth of modern spiritualism in America in the mid-19th century.
Along the way, Keene also coins a useful term -- 'true-believer syndrome.' He applies it to the customers (or dupes, or rubes) who continue to believe that they've experienced real spiritual phenomena even when, in some cases, the medium himself or herself comes clean and admits to that person that everything was a fraud. I think you can imagine how this phenomenon plays out again and again in areas other than spiritualism. A fascinating book about a fascinating (and disturbing) topic. Recommended.