“No,” he almost shouted.  Of a sudden it seemed to dawn on him what Kennedy was driving at—­the robbery of his own house with no loss except of a packet of letters on business, followed by the attempt on Mrs. Hollingsworth.  “Do you think I’d keep dynamite, even in the safe?”

To hide his confusion he had turned and was bending again over the engine.

“How is it?” asked Kennedy, his signaling over.

“Able to run on four cylinders and one propeller,” replied Verplanck.

“Then let’s try her.  Watch the engine.  I’ll take the wheel.”

Limping along, the engine skipping and missing, the once peerless Streamline started back across the bay.  Instead of heading toward the club, Kennedy pointed her bow somewhere between that and Verplanck’s.

“I wish Armand would get busy,” he remarked, after glancing now and then in the direction of the club.  “What can be the matter?”

“What do you mean?” I asked.

There came the boom as if of a gun far away in the direction in which he was looking, then another.

“Oh, there it is.  Good fellow.  I suppose he had to deliver my message to Mrs. Hollingsworth himself first.”

From every quarter showed huge balls of fire, rising from the sea, as it were, with a brilliantly luminous flame.

“What is it?” I asked, somewhat startled.

“A German invention for use at night against torpedo and aeroplane attacks.  From that mortar Armand has shot half a dozen bombs of phosphide of calcium which are hurled far into the darkness.  They are so constructed that they float after a short plunge and are ignited on contact by the action of the salt water itself.”

It was a beautiful pyrotechnic display, lighting up the shore and hills of the bay as if by an unearthly flare.

“There’s that thing now!” exclaimed Kennedy.

In the glow we could see a peculiar, birdlike figure flying through the air over toward the Hollingsworth house.  It was the hydroaeroplane.

Out from the little stretch of lawn under the accentuated shadow of the trees, she streaked into the air, swaying from side to side as the pilot operated the stabilizers on the ends of the planes to counteract the puffs of wind off the land.

How could she ever be stopped?

The Streamline, halting and limping, though she was, had almost crossed the bay before the light bombs had been fired by Armand.  Every moment brought the flying boat nearer.

She swerved.  Evidently the pilot had seen us at last and realized who we were.  I was so engrossed watching the thing that I had not noticed that Kennedy had given the wheel to Verplanck and was standing in the bow, endeavoring to sight what looked like a huge gun.

In rapid succession half a dozen shots rang out.  I fancied I could almost hear the ripping and tearing of the tough rubber-coated silken wings of the hydroaeroplane as the wind widened the perforation the gun had made.