I believe, is the dagger." He held it up, and Alison gave a faint
cry of astonishment and dismay. Sullivan's face grew ghastly, and he sat
down weakly on the nearest chair.

The detective looked at him shrewdly, then at Alison's agitated face.

"Where have you seen this dagger before, young lady?" he asked, kindly
enough.

"Oh, don't ask me!" she gasped breathlessly, her eyes turned on
Sullivan. "It's--it's too terrible!"

"Tell him," I advised, leaning over to her. "It will be found out later,
anyhow."

"Ask him," she said, nodding toward Sullivan. The detective unwrapped
the small box Alison had brought, disclosing the trampled necklace and
broken chain. With clumsy fingers he spread it on the table and fitted
into place the bit of chain. There could be no doubt that it belonged
there.

"Where did you find that chain?" Sullivan asked hoarsely, looking for
the first time at Alison.

"On the floor, near the murdered man's berth."

"Now, Mr. Sullivan," said the detective civilly, "I believe you can
tell us, in the light of these two exhibits, who really did murder Simon
Harrington."

Sullivan looked again at the dagger, a sharp little bit of steel with
a Florentine handle. Then he picked up the locket and pressed a hidden
spring under one of the cameos. Inside, very neatly engraved, was the
name and a date.

"Gentlemen," he said, his face ghastly, "it is of no use for me to
attempt a denial. The dagger and necklace belonged to my sister, Alice
Curtis!"

CHAPTER XXXI. AND ONLY ONE ARM

Hotchkiss was the first to break the tension.

"Mr. Sullivan," he asked suddenly, "was your sister left-handed?"

"Yes."

Hotchkiss put away his note-book and looked around with an air of
triumphant vindication. It gave us a chance to smile and look relieved.
After all, Mrs. Curtis was dead. It was the happiest solution of the
unhappy affair. McKnight brought Sullivan some whisky, and he braced up
a little.

"I learned through the papers that my wife was in a Baltimore hospital,
and yesterday I ventured there to see her. I felt if she would help me
to keep straight, that now, with her father and my sister both dead, we
might be happy together.

"I understand now what puzzled me then. It seemed that my sister went
into the next car and tried to make my wife promise not to interfere.
But Ida--Mrs. Sullivan--was firm, of course. She said her father had
papers, certificates and so on, that would stop the marriage a