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."

"I can conceive of no explanation."

"And yet there should be no combination of events for which the wit of
man cannot conceive an explanation. Simply as a mental exercise,
without any assertion that it is true, let me indicate a possible line
of thought. It is, I admit, mere imagination; but how often is
imagination the mother of truth?

"We will suppose that there was a guilty secret, a really shameful
secret in the life of this man Douglas. This leads to his murder by
someone who is, we will suppose, an avenger, someone from outside. This
avenger, for some reason which I confess I am still at a loss to
explain, took the dead man's wedding ring. The vendetta might
conceivably date back to the man's first marriage, and the ring be
taken for some such reason.

"Before this avenger got away, Barker and the wife had reached the
room. The assassin convinced them that any attempt to arrest him would
lead to the publication of some hideous scandal. They were converted to
this idea, and preferred to let him go. For this purpose they probably
lowered the bridge, which can be done quite noiselessly, and then
raised i