The Sacred Herb by Fergus Hume — Read

In the exercise of his profession, a legitimate detective would have waited to question Mrs. Rover. Since she had said so much he would have forced her to say all, in order to get at the truth as speedily as possible; but Lord Prelice was new to the business, and his emotions were not entirely under control. On leaving Alexander Mansions he felt that he was in possession of a most dangerous and perilous secret, the publication of which would cause even a greater sensation than that produced by the crimes themselves. The shock of learning that Mrs. Rover was the woman who had been brought by Agstone into Number Forty was very great, and quite confused Prelice's usually strong brain. He did not dare to call again on Shepworth, lest he should say too much.

It will be seen that Prelice, being an untrained detective, jumped somewhat hastily to a conclusion. Mrs. Rover had admitted that she wore the dress, the mask, and the domino which Shepworth had seen on the unknown lady. But Constance did not know that Ned had so described her appearance, and, if she had, would probably not have admitted that she had assumed such a costume at her _bal masque_. But the mere fact that, even in ignorance of Shepworth's description, she had, as the saying goes, given herself away, should have proved to Lord Prelice that she could not be guilty. Had Mrs. Rover entered Number Forty in Agstone's company, and had she struck the blow, she assuredly would not have incriminated herself so unthinkingly. Rather would she have denied that the frock mentioned by Prelice belonged to her.