“Our next obvious step is to check, so far as we can, the movements of Mortimer Tregennis after he left the room. In this there is no difficulty, and they seem to be above suspicion. Knowing my methods as you do, you were, of course, conscious of the somewhat clumsy water-pot expedient by which I obtained a clearer impress of his foot than might otherwise have been possible. The wet, sandy path took it admirably. Last night was also wet, you will remember, and it was not difficult—having obtained a sample print—to pick out his track among others and to follow his movements. He appears to have walked away swiftly in the direction of the vicarage.

“If, then, Mortimer Tregennis disappeared from the scene, and yet some outside person affected the card-players, how can we reconstruct that person, and how was such an impression of horror conveyed? Mrs. Porter may be eliminated. She is evidently harmless. Is there any evidence that someone crept up to the garden window and in some manner produced so terrific an effect that he drove those who saw it out of their senses? The only suggestion in this direction comes from Mortimer Tregennis himself, who says that his brother spoke about some movement in the garden. That is certainly remarkable, as the night was rainy, cloudy, and dark. Anyone who had the design to alarm these people would be compelled to place his very face against the glass before he could be seen. There is a three-foot flower-border outside this window, but no indication of a footmark. It is difficult to imagine, then, how an outsider could have made so terrible an impression upon the company, nor have we found any possible motive for so strange and elaborate an attempt. You perceive our difficulties, Watson?”