Hello.

According to a Conan Doyle website:

'...By 1916, Conan Doyle's explorations into psychic matters had
convinced him that he should devote the final years of his life to
the advancement of Spiritualism. He began to write extensively on the
subject, and to travel the world with his family promoting his
beliefs. From those who had lost loved ones during the First World
War he found a ready acceptance for his arguments, but his beliefs
were to bring him into conflict with many people during the course of
the final thirteen years of his life.

'Spiritualism became Conan Doyle's religion and his driving force,
taking him to Australia, America, Canada, and South Africa for
lecture tours which he recorded in various biographical studies. He
was careful in his testing of mediums but, not unnaturally, those
cases where he was deceived have been seized upon by critics to
justify what they regard as his credulity. Credulity was a charge
also to be levelled at Conan Doyle when, in 1922, he declared the
famous Cottingley Fairy photographs to be genuine. This latter case
has been frequently documented, and the photographs are famous the
world over.'

I believe people can communicate with the dead via the planchette.
Though I read some of his major historical novels, 'The White
Company' and 'Sir Nigel,' I didn't find them as interesting as his
major fictional creations, Sherlock Holmes, Professor Challenger, and
Brigadier Gerard. Doyle created a supernatural atmosphere in stories
like 'The Hound of the Baskervilles,' but doesn't seem to have
written much about the occult.

~Ashoke