Found: the elementary answers to questions about Holmes's creator

Four decades after they were last seen, an archive of letters and manuscripts belonging to Sir Arthur Conan Doyle has surfaced at a legal firm in London.

The last mention of the papers was in the authorised biography of the creator of Sherlock Holmes, by John Dickson Carr, in 1949.

The papers will go on display in May before 3,000 items are auctioned by Christie's, London, on 19 May. They are expected to fetch £2m.

Some items, particularly letters to his mother, will go to the British Library under the terms of a family bequest. The Government cannot stop other parts from leaving the country as they have been largely kept in Switzerland since Conan Doyle's death in 1930.

Tom Lamb, Christie's head of books and manuscripts, said the letters would allow a re-evaluation of Conan Doyle's relationships with family members, and his fierce advocacy of spiritualism.

Jane Flower, a manuscripts consultant for Christie's, said there was much previously unknown material relating to Conan Doyle the man. His son, Adrian, had filtered what had been available. "Adrian Conan Doyle kept a very close watch on what people wrote about his father and censored material to make certain his father was shown in the best light," she said.

Many of the papers relate to causes he espoused, including miscarriages of justice such as the Edalji case, which involved a young Parsi lawyer wrongly convicted of murder. Other letters in the archive shed light on his relationship with his public, including correspondences with fans who sent their own mysteries to be solved, such as the "mystery of the missing fiancé".

Also included is correspondence with his brother Innes, his sister Lottie, Winston Churchill, Oscar Wilde, George Bernard Shaw, PG Wodehouse and the American president Theodore Roosevelt.