Again, who would have supposed from the early part of _Great Expectations_ that Estella was the daughter of Abel Magwitch? {196} In _Barnaby Rudge_, Maypole Hugh turns out to be an illegitimate son of Sir John Chester. In _The Old Curiosity Shop_, ‘The Stranger’ is found to be the brother of the Grandfather. In _Bleak House_, Esther Summerson is revealed as a daughter of Lady Dedlock. In _Our Mutual Friend_, John Rokesmith turns out to be John Harmon. That the action of opium had a part to play in the revelation can hardly be doubted. The whole book is drenched in opium. In _The Moonstone_ the problem is who stole the jewels. It is solved by opium. The jewels are stolen by a man under the influence of opium surreptitiously administered. He is quite unconscious of what he has done, and remains unconscious. Afterwards he is discovered by a fresh administration of opium. When the opium has completely done its work the man repeats his deed, and the experiment is conclusive. I do not think that any one reading right on would name the perpetrator of the theft, and yet when we take a backward glance we find an account of a dinner-party about the seventieth page which gives the clue. I doubt whether any one on first reading it would see in it anything that mattered, and yet it contains everything that matters. The height of art in work like this is to conceal art. You may be able at an early stage to introduce facts which contain the ultimate solution of your problem, and yet appear important enough to be stated for their own sake. The solution of the problem, or rather the materials of the solution, should be given, and yet the reader should be unable to detect the full significance of the preliminary statement till the complete clearing arrives. At the same time the book will not be satisfactory if details are superfluous, if they do nothing to carry one on to the dissipation of the mystery. It is not to be denied that this fitting of everything into its place is at times a little wearisome. ‘The construction is most minute and most wonderful,’ wrote Anthony Trollope of Wilkie Collins. ‘I can never lose the taste of the construction. The author seems always warning me to remember that something happened at exactly half-past two on Tuesday morning, or that a woman disappeared from the road just fifteen yards beyond the fourth milestone.’ There is truth in this, but if Anthony Trollope had written a novel of mystery, which perhaps he could never have done, he would have had to take the same path.