“Oh, yes!” she answered; “I spent three months there once, and this place is like it.”

“Was it a happy time?” I inquired, jealous of those tears.

“It was a hateful time,” she said, vehemently.  “Don’t let us talk of it.  I hate to remember it.  Why cannot we forget things, Dr. Martin?  You, who are so clever, can tell me that.”

“That is simple enough,” I said, smiling.  “Every circumstance of our life makes a change in the substance of the brain, and, while that remains sound and in vigor, we cannot forget.  To-day is being written on our brain now.  You will have to remember this, Olivia.”

“I know I shall remember it,” she answered, in a low tone.

“You have travelled a great deal, then?” I pursued, wishing her to talk about herself, for I could scarcely trust my resolution to wait till we were out of the caves.  “I love you with all my heart and soul” was on my tongue’s end.

“We travelled nearly all over Europe,” she replied.

I wondered whom she meant by “we.”  She had never used the plural pronoun before, and I thought of that odious woman in Guernsey—­an unpleasant recollection.

We had wandered back to the opening where Tardif had left us.  The rapid current between us and Breckhou was running in swift eddies, which showed the more plainly because the day was calm, and the open sea smooth.  Olivia stood near me; but a sort of chilly diffidence had crept over me, and I could not have ventured to press too closely to her, or to touch her with my hand.

“How have you been content to live here?” I asked.

“This year in Sark has saved me,” she answered, softly.

“What has it saved you from?” I inquired, with intense eagerness.  She turned her face full upon me, with a world of reproach in her gray eyes.

“Dr. Martin,” she said, “why will you persist in asking me about my former life?  Tardif never does.  He never implies by a word or look that he wishes to know more than I choose to tell.  I cannot tell you any thing about it.”

I felt uncomfortably that she was drawing a comparison unfavorable to me between Tardif and myself—­the gentleman, who could not conquer or conceal his desire to fathom a mystery, and the fisherman, who acted as if there were no mystery at all.  Yet Olivia appeared more grieved than offended; and when she knew how I loved her she would admit that my curiosity was natural.  She should know, too, that I was willing to take her as she was, with all the secrets of her former life kept from me.  Some day I would make her own I was as generous as Tardif.

Just then my ear caught for the first time a low boom-boom, which had probably been sounding through the caves for some minutes.

“Good Heavens!” I ejaculated.