“You think then, definitely, that Barker and Mrs. Douglas are guilty of the murder?”

“There is an appalling directness about your questions, Watson,” said Holmes, shaking his pipe at me.  “They come at me like bullets.  If you put it that Mrs. Douglas and Barker know the truth about the murder, and are conspiring to conceal it, then I can give you a whole-souled answer.  I am sure they do.  But your more deadly proposition is not so clear.  Let us for a moment consider the difficulties which stand in the way.

“We will suppose that this couple are united by the bonds of a guilty love, and that they have determined to get rid of the man who stands between them.  It is a large supposition; for discreet inquiry among servants and others has failed to corroborate it in any way.  On the contrary, there is a good deal of evidence that the Douglases were very attached to each other.”

“That, I am sure, cannot be true,” said I, thinking of the beautiful smiling face in the garden.

“Well at least they gave that impression.  However, we will suppose that they are an extraordinarily astute couple, who deceive everyone upon this point, and conspire to murder the husband.  He happens to be a man over whose head some danger hangs—­”

“We have only their word for that.”

Holmes looked thoughtful.  “I see, Watson.  You are sketching out a theory by which everything they say from the beginning is false.  According to your idea, there was never any hidden menace, or secret society, or Valley of Fear, or Boss MacSomebody, or anything else.  Well, that is a good sweeping generalization.  Let us see what that brings us to.  They invent this theory to account for the crime.  They then play up to the idea by leaving this bicycle in the park as proof of the existence of some outsider.  The stain on the windowsill conveys the same idea.  So does the card on the body, which might have been prepared in the house.  That all fits into your hypothesis, Watson.  But now we come on the nasty, angular, uncompromising bits which won’t slip into their places.  Why a cut-off shotgun of all weapons—­and an American one at that?  How could they be so sure that the sound of it would not bring someone on to them?  It’s a mere chance as it is that Mrs. Allen did not start out to inquire for the slamming door.  Why did your guilty couple do all this, Watson?”

“I confess that I can’t explain it.”

“Then again, if a woman and her lover conspire to murder a husband, are they going to advertise their guilt by ostentatiously removing his wedding ring after his death?  Does that strike you as very probable, Watson?”

“No, it does not.”

“And once again, if the thought of leaving a bicycle concealed outside had occurred to you, would it really have seemed worth doing when the dullest detective would naturally say this is an obvious blind, as the bicycle is the first thing which the fugitive needed in order to make his escape.”