Marjorie Marlowe, alert, swung the bottle of champagne in its silken net on a silken cord and it crashed on the bow as she cried, gleefully, “I christen thee Usona!”

Down the ship slid, with a slow, gliding motion at first, rapidly gathering headway.  As her stern sank and finally the bow dipped into the water, cheers broke forth.  Then a cloud of smoke hid her.  There was an ominous silence.  Was she wrecked, at last, after all?  A puff of wind cleared the smoke.

“Just the friction of the ways—­set the grease on fire,” shouted Marlowe.  “It always does that.”

Wedges, sliding ways, and other parts of the cradle floated to the surface.  The tide took her and tugs crept up and pulled her to the place selected for temporary mooring.  A splash of a huge anchor, and there she rode—­safe!

In the revulsion of feeling, every eye on the platform turned involuntarily to Kennedy.  Marlowe, still holding his hand, was speechless.  Marjorie leaned forward, almost hysterical.

“Just a moment,” called Craig, as some turned to go down.  “There is just one thing more.”

There was a hush as the crowd pressed close.

“There’s a conspiracy here,” rang out Craig’s voice, boldly, “a foreign trade war.  From the start I suspected something and I tried to reason it out.  Having failed to stop the work, failed to kill Marlowe—­what was left?  Why, the launching.  How?  I knew of that motor-boat.  What else could they do with it?  I thought of recent tests that have been made with express cruisers as mine-planters.  Could that be the scheme?  The air-boat scheme occurred to me late last night.  It at least was worth trying.  You see what has happened.  Now for the reckoning.  Who was their agent?  I have something here that will interest you.”

Kennedy was speaking rapidly.  It was one of those occasions in which Kennedy’s soul delighted.  Quickly he drew a deft contrast between the infinitely large hulk of the Usona as compared to the infinitely small bacteria which he had been studying the day before.  Suddenly he drew forth from his pocket the bullet that had been fired at Marlowe, then, to the surprise of even myself, he quietly laid a delicate little nail file and brush in the palm of his hand beside the bullet.

A suppressed cry from Rae Melzer caused me to recollect the file and brush she had missed.

“Just a second,” raced on Kennedy.  “On this file and brush I found spores of those deadly anaerobes—­dead, killed by heat and an antiseptic, perhaps a one-per-cent. solution of carbolic acid at blood heat, ninety-eight degrees—­dead, but nevertheless there.  I suppose the microscopic examination of finger-nail deposits is too minute a thing to appeal to most people.  But it has been practically applied in a number of criminal cases in Europe.  Ordinary washing and even cleaning doesn’t alter microscope findings.  In this case this trifling clue is all that leads to the real brain of this plot, literally to the hand that directed it.”  He paused a moment.