Tracked by a Tattoo by Fergus Hume

Fanks was rather astonished when he learned that Mrs. Boazoph had contrived the lure which had drawn Fellenger to his death. He had given the landlady credit for more cleverly concealing her scheme, and that she should have carried out a plan so compromising, in so open a manner, seemed to him to be the height of folly. Nevertheless, he was pleased that he had discovered who had directed the fatal envelope; and he was still more pleased that Mrs. Boazoph had sent for Hersham. If possible he intended to learn her reason for seeking an interview, and to ascertain why she had fainted at the intelligence that Hersham was likely to be arrested for committing the crime. A true report of that conversation -- and Fanks had no doubt that Hersham would repeat it faithfully to him -- might afford the clue to the mystery. At the present moment Fanks was convinced that the landlady of the Red Star could unravel the riddle if she chose, and he was resolved to force her to do so.

But here an element on which Fanks had not calculated came into play.