The Dark House by George Manville Fenn

An extremely wealthy but reclusive man has died, leaving an eccentric will which hints at great riches hidden somewhere in the house. Most of the people at the reading of the will did not know the deceased in person, but had received kindnesses from him, for instance by the payment of school and university fees. The principal beneficiary, a great-nephew, also did not know him. The only two people who really knew him were the old lawyer who dealt with his affairs, and an old Indian servant. Yet when the will had been read, and they all went to where the treasure–gold, jewels and bank-notes–were supposed to be hidden, nothing could be found.