Denison had scarcely gone to arrange for some one to watch the office that night, when Kennedy, having gathered up his radioscope and packed into a parcel a few other things from various cabinets, announced:  “Walter, I must see that Miss Wallace, right away.  Denison has already given me her address.  Call a cab while I finish clearing up here.  I don’t like the looks of this thing, even if Haughton does neglect it.”

We found Miss Wallace at a modest boarding-house in an old but still respectable part of the city.  She was a very pretty girl, of the slender type, rather a business woman than one given much to amusement.  She had been ill and was still ill.  That was evident from the solicitous way in which the motherly landlady scrutinized two strange callers.

Kennedy presented a card from Denison, and she came down to the parlor to see us.

“Miss Wallace,” began Kennedy, “I know it is almost cruel to trouble you when you are not feeling like office work, but since the robbery of the safe at Pittsburgh, there have been threats of a robbery of the New York office.”

She started involuntarily, and it was evident, I thought, that she was in a very high-strung state.

“Oh,” she cried, “why, the loss means ruin to Mr. Denison!”

There were genuine tears in her eyes as she said it.

“I thought you would be willing to aid us,” pursued Kennedy sympathetically.  “Now, for one thing, I want to be perfectly sure just how much radium the Corporation owns, or rather owned before the first robbery.”

“The books will show it,” she said simply.

“They will?” commented Kennedy.  “Then if you will explain to me briefly just the system you used in keeping account of it, perhaps I need not trouble you any more.”

“I’ll go down there with you,” she answered bravely.  “I’m better to-day, anyhow, I think.”

She had risen, but it was evident that she was not as strong as she wanted us to think.

“The least I can do is to make it as easy as possible by going in a car,” remarked Kennedy, following her into the hall where there was a telephone.

The hallway was perfectly dark, yet as she preceded us I could see that the diamond pin which held her collar in the back sparkled as if a lighted candle had been brought near it.  I had noticed in the parlor that she wore a handsome tortoiseshell comb set with what I thought were other brilliants, but when I looked I saw now that there was not the same sparkle to the comb which held her dark hair in a soft mass.  I noticed these little things at the time, not because I thought they had any importance, but merely by chance, wondering at the sparkle of the one diamond which had caught my eye.

“What do you make of her?” I asked as Kennedy finished telephoning.

“A very charming and capable girl,” he answered noncommittally.

“Did you notice how that diamond in her neck sparkled?” I asked quickly.