Dark Clue

'This is a book begun, but not finished. I could not finish it. Many times I have come close to destroying it, thinking I should have no rest while it remained to reproach me. I could not bring myself to do it. I have therefore given instructions that it should be sealed in a box, which is to remain unopened until I, my wife Laura, our sister Marion Halcombe, and all our children are dead.'So begi...