ked, as Craig rejoined me a few moments later.
"What did you say? My hat's off to you," I added in admiration.

"Told him I had trailed her here with one of my operatives, but was
convinced there was nothing wrong, after all," he returned.

"You mean," I asked as the result of Craig's quick thinking dawned on
me, "that you told him Sherburne was _your_ operative?"

Kennedy nodded. "I want to see him, now, if I can," he said simply.

CHAPTER VI

THE SERUM DIAGNOSIS

We paid our check and Kennedy and I sauntered in the direction Sherburne
had taken, finding him ultimately in the cafe, alone. Without further
introduction Kennedy approached him.

"So--you are a detective?" sneered Sherburne superciliously, elevating
his eyebrows just the fraction of an inch.

"Not exactly," parried Kennedy, seating himself beside Sherburne. Then
in a tone as if he were willing to get down, without further
preliminary, to business, seemingly negotiating, he asked: "Mr.
Sherburne, may I ask just what it is on which you base your claim on
Mrs. Seabury? Is it merely meeting her here? If that is so you must know
that it amounts to nothing--now."

The two men faced each other, each taking the other's measure.

"Nothing?" coolly retorted Sherburne. "Perhaps not--in itself.
But--suppose--I--had--"

He said the words slowly, as he fumbled in his fob pocket, then cut them
short as he found what he was looking for. Safely, in the palm of his
hand, he displayed a latch-key, momentarily, then with a taunting smile
dropped it back again into the fob pocket.

"Perhaps she gave it to me--perhaps I was a welcome visitor in her
apartment," he insinuated. "How would she relish having that told to
Mr. Seabury--backed up by the possession of the key?"

I could not help feeling that for the moment Kennedy was checkmated.
Sherburne was playing a desperate game and apparently held the key,
however he got it, as a trump card.

"Thank you," was all that Kennedy said, as he rose. "I wanted to know
how far you could go. Perhaps we can meet you halfway."

Sherburne smiled cynically. "All the way," he said quietly, as we left
the cafe.

In silence Kennedy left the hotel and jumped into a cab, directing the
driver to the laboratory, where he had asked Mrs. Seabury to wait for
him. We found her there, still much agitated.

Hastily Craig explained to her how he had saved the situation, but her
mind was too occupied over something else to pay mu