“Have you found anything?” I managed to ask, finally.

“Yes, indeed,” he nodded, thoughtfully.  “I shadowed Kato from the Forum.  It must have been before Miss Langdale came out that he left.  He lives down-town in a tenement-house.  There’s something queer about that Jap.”

“I think there is,” I agreed.  “I don’t like his looks.”

“But it wasn’t he who interested me so much to-night,” Craig went on, ignoring my remark, “as a woman.”

“A woman?” I queried, in surprise.  “A Jap, too?”

“No, a white woman, rather good-looking, too, with dark hair and eyes.  She seemed to be waiting for him.  Afterward I made inquiries.  She has been seen about there before.”

“Who was she?” I asked, fancying perhaps Miss Langdale had made another visit while she was out, although from the time it did not seem possible.

“I followed her to her house.  Her name is Hackstaff—­”

“The first trained nurse!” I exclaimed.

“Miss Hackstaff is an enigma,” confessed Kennedy.  “At first I thought that perhaps she might be one of those women whom the Oriental type fascinated, that she and Kato might be plotting.  Then I have considered that perhaps her visits to Kato may be merely to get information—­that she may have an ax to grind.  Both Kato and she will bear watching, and I have made arrangements to have it done.  I’ve called on that young detective, Chase, whom I’ve often used for the routine work of shadowing.  There’s nothing more that we can do now until to-morrow, so we might as well turn in.”

Early the next day Kennedy was again at work, both in his own laboratory and in that of the Health Department, making further studies of the food and the effect it had on the pigeons, as well as observing what changes were produced by the white tablets he had extracted from the yeast.

It was early in the forenoon when the buzzer on the laboratory door sounded and I opened the door to admit Chase in a high state of excitement.

“What has happened?” asked Craig, eagerly.

“Many things,” reported the young detective, breathlessly.  “To begin with, I followed Miss Hackstaff from her apartment this morning.  She seemed to be worked up over something—­perhaps had had a sleepless night.  As nearly as I could make out she was going about aimlessly.  Finally, however, I found that she was getting into the neighborhood of Doctor Aitken and of the Forum.  Well, when we got to the Forum she stopped and waited in front of it—­ oh, I should say almost half an hour.  I couldn’t make out what it was she wanted, but at last I found out.”

He paused a moment, then raced on, without urging.  “Miss Langdale came out—­and you should have seen the Hackstaff woman go for her.”  He drew in his breath sharply at the reminiscence.  “I thought there was going to be a murder done—­on Riverside Drive.  Miss Langdale screamed and ran back into the apartment.  There was a good deal of confusion.  The hall-boys came to the rescue.  In the excitement, I managed to slip into the elevator with her.  No one seemed to think it strange then that an outsider should be interested.  I went up with her—­saw Wardlaw, as she poured out the story.  He’s a queer one.  Is he right?” “Why?” asked Craig, indulgently.