The Opal Serpent by Fergus Hume — Read

After all, Hurd did not send Jessop to town as he threatened to do. Evidently the captain had told him all he knew, and appeared to be innocent of Krill's death. But, in spite of his apparent frankness the detective had an idea that something was being kept back, and what that something might be, he determined to find out. However, his thoughts were turned in another direction by a note from Beecot addressed to him at "The Red Pig," asking him to come at once to the Jubileetown Laundry. "I believe we have discovered the person who stole the opal brooch from me," wrote Paul, "and Deborah has made a discovery connected with Norman which may prove to be of service."

Wondering what the discovery might be, and wondering also who had taken the brooch, Hurd arranged that Jessop and Hokar should remain at Christchurch under the eyes of two plain-clothes officials. These managed their duties so dexterously that Matilda Junk was far from guessing what was going on. Moreover, she informed the detective, who she thought was a commercial gent, that she intended to pay a visit to her sister, Mrs. Tawsey, and demanded the address, which Hurd gave readily enough. He thought that if Matilda knew anything -- such as the absence of Mrs. Krill from the hotel during the early part of July -- Deborah might induce her to talk freely.