“I met Conyers the other day,” Granet proceeded, “the man who commands the Scorpion. I managed to get an invitation down to Portsmouth to have lunch with him on his ship.  I went down with his sister and the young lady he is engaged to marry.  On deck there was a structure of some sort covered up.  I tried to make inquires about it but they headed me off pretty quick.  There was even a sentry standing on guard before it—­wouldn’t let me even feel the shape of it.  However, I hadn’t given up hope when there came a wireless—­no guests to be allowed on board.  Conyers had to pack us all off back to the hotel, without stopping even for lunch.  From the hotel I got a telescope and I saw a pinnace with half-a-dozen workmen, and a pilot who was evidently an engineer, land on board.  They seemed to be completing the adjustments of some new piece of mechanism.  Then they steamed away out of sight of the land.”

“A busy life, yours, Ronnie,” Sir Alfred remarked, after a moments pause.  “What about it now?  I’ve had two urgent messages from Berlin this morning.”

“It’s pretty difficult,” Granet acknowledged.  “The Scorpion’s out in the Channel or the North Sea.  No getting at her.  And I don’t believe there’s another destroyer yet fitted with this apparatus, whatever it may be.”

“They must be making them somewhere, though,” Sir Alfred remarked.

His nephew nodded.

“To think,” he muttered, “that we’ve two hundred men spread out at Tyneside, Woolwich and Portsmouth, and not one of them got on to this!  A nation of spies, indeed!  They’re mugs, uncle.”

“Not altogether that,” the banker replied.  “We have some reports, although they don’t go far enough.  I can put you on to the track of the thing.  The apparatus you saw is something in the nature of an inverted telescope, with various extraordinary lenses treated by a new process.  You can see forty feet down under the surface of the water for a distance of a mile, and we believe that attached to the same apparatus is an instrument which brings any moving object within the range of what they call a deep-water gun.”

“Did that come from reports?” Granet asked eagerly.

“It did,” Sir Alfred said.  “Further than that, the main part of the instrument is being made under the supervision of Sir Meyville Worth, in a large workshop erected on his estate in a village near Brancaster in Norfolk.”

“I take it back,” Granet remarked.

“The plans of the instrument should be worth a hundred thousand pounds,” Sir Alfred continued calmly.  “If that is impossible, the destruction of the little plant would be the next consideration.”

“Do I come in here?” Granet inquired.