“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 it again. He made his escape, and for some reason thought that he could do so more safely on foot than on the bicycle. He therefore left his machine where it would not be discovered until he had got safely away. So far we are within the bounds of possibility, are we not?”
“Well, it is possible, no doubt,” said I, with some reserve.
“We have to remember, Watson, that whatever occurred is certainly something very extraordinary. Well, now, to continue our supposititious case, the couple—not necessarily a guilty couple—realize after the murderer is gone that they have placed themselves in a position in which it may be difficult for them to prove that they did not themselves either do the deed or connive at it. They rapidly and rather clumsily met the situation. The mark was put by Barker’s bloodstained slipper upon the windowsill to suggest how the fugitive got away. They obviously were the two who must have heard the sound of the gun; so they gave the alarm exactly as they would have done, but a good half hour after the event.”
“And how do you propose to prove all this?”