"How long ago did Hoefer leave?" I asked.

"About an hour, I think. He has locked the door of the morning-room and taken the key with him," she added, laughing.

She presented a pretty picture, indeed, in that half-darkened room, leaning back gracefully and smiling upon me.

"He announced no fresh discovery?"

"He spoke scarcely a dozen words."

"But this mystery is a very disagreeable one for you who live here. I presume that you live with your cousin always?"

"Yes," she responded. "After my father's death, some years ago, I came here to live with her."

So her father was dead! The Tempter was not, as I had all along suspected, her father.

I longed to take her in my arms and tell her the truth, that I was actually her husband and that I loved her. Yet, how could I? The mystery was so complicated, and so full of inscrutable points, that to make any such declaration must only fill her with fear of myself.

We chatted on while I feasted my eyes upon her wondrous beauty. Had she, I asked myself, ever seen young Chetwode since her return to London? Did she really love him, or was he merely the harmless but necessary admirer which every girl attracts towards herself as a sort of natural instinct? The thought of him caused a vivid recollection of that night in Whitton Park to arise within me.

Where was Tattersett--the man who had laughed at her when she had declared her intention of escaping him by suicide? Who was he? What was he?

It occurred to me, now that I had learned some potent facts from her own lips, that my next course should be to find this man and investigate his past. By doing so I might elucidate the problem.

Her ladyship, with a cry of welcome upon her lips, entered the room and sank, hot and fatigued, into a cosy armchair.

"London is simply unbearable!" she declared. "It's ever so many degrees hotter than at Atworth, and in the Stores it is awfully stuffy. In the provision department b.u.t.ter, bacon, and things seem all melting away."

"You'll be glad to get back again to Wiltshire," I laughed.

"Very. We shall go by the night-mail to-morrow," she answered. "Why don't you come up and visit us, Doctor? My husband would be charmed to meet you I'm sure."

"That's just what I've been saying, dear," exclaimed Beryl. "Do persuade Doctor Colkirk to come."

"I am sure you are both very kind," I replied, "but at present I am in practice."

"You can surely take a holiday," urged Beryl. "Do come. We would try to make it pleasant for you."

Her persuasion decided me, and, after some further pressing on the part of her ladyship, I accepted the invitation with secret satisfaction, promising to leave in the course of a week or ten days.

Then we fell to discussing the curious phenomena of the previous night, until, having again exhausted the subject, I rose to take my leave.

"Good-bye, Doctor Colkirk," Beryl said, looking into my eyes as I held her small hand. "I hope we shall soon meet down in Wiltshire, and, when we do, let us forget all the mystery of yesterday."

"I suppose you have given Hoefer permission to visit, the room when he wishes to pursue his investigations?" I said, turning to her ladyship.

"Of course. The house is entirely at his disposal. One does not care to have a death-trap in one's own house."

"He will do his best--of that I feel quite sure," I said.

And then again promising to visit her soon, I shook her hand, bade them both adieu, and with a last look at the frail, graceful woman I loved, went out into the hot, dusty street.

In order to celebrate my sudden accession to wealth I lunched well at Simpson's, and then took a hansom to old Hoefer's dismal rooms in.

Bloomsbury. To me, so gloomy and severe is that once-aristocratic district that, in my hospital days, I called it Gloomsbury.

Hoefer occupied a dingy flat in Museum Mansions, and, as I entered the small room which served him as laboratory, I was almost knocked back by the choking fumes of some acid with which he was experimenting. A dense blue smoke hung over everything, and through it loomed the German's great fleshy face and gold-rimmed spectacles. He was in his shirt-sleeves, seated at a table, watching some liquid boiling in a big gla.s.s retort. Around his mouth and nose a damp towel was tied, and as I entered he motioned me back.

"Ach! don't come in here, my tear Colkirk! I vill come to you. Ze air is not good just now. Wait for me there in my room."

Heedless of his warning, however, I went forward to the table, coughing and choking the while. I took out my handkerchief, when suddenly he s.n.a.t.c.hed it from me, and steeped it in some pale yellow solution. Then, when I placed it before my mouth, inhaling it, I experienced no further difficulty in respiration.

The nature of the experiment on which he was engaged I could not determine. From the retort he was condensing those suffocating fumes, drop by drop, now and then dipping pieces of white, prepared paper into the liquid thus obtained. I stood by watching in silence.

Once he placed a drop of that liquid upon a gla.s.s slide, dried it for crystallisation, and, placing it beneath the microscope, examined it carefully.

He grunted. And I knew he was not satisfied.

Then he added a few drops of some colourless liquid to that in the retort, and the solution at once a.s.sumed a pale green hue. He boiled it again for three minutes by his common, metal watch, then, having drained it off into a shallow gla.s.s bowl to cool, blew out his lamp, and I followed him back into his small, cosy, but rather stuffy little den.

"Well?" he inquired. "You have called at her ladyship's--eh?"

"Yes," I replied, stretching myself in one of his rickety chairs; "but you were there before me. What have you discovered?"

"Nothing."

"But that experiment I have just witnessed? Has it no connexion with the mystery?"

"Yes, some slight connexion. It was, however, a failure," he grunted, still speaking with his strong accent.

"You experienced the same sensation there to-day, I hear?" I said.

"H'm, yes; but not so strong."

"And the same injection cured you?"

"Of course. That, however, tells us nothing. We cannot yet ascertain how it is caused."

"Or find out who was that unknown woman in black," I added.

"If we could discover her we might obtain the key to the situation," he responded.

"I have been invited by her ladyship to visit them in Wiltshire," I said suddenly, as I lit a cigarette, "and I have accepted. Have I done right, do you think?"

"You would have done far better to stay here in London," grunted the old man. "If we mean to get at the bottom of this mystery we must work together."

"How?"

"In this affair, my dear Colkirk," he exclaimed, with a sudden burst of confidence, "there is much more than of what we are aware. There is some motive in getting rid of Miss Wynd secretly and surely. I feel certain that she knows who her mysterious visitor was, but dare not tell us."

"I am going down to Atworth," I said. "Perhaps I shall discover something."