“Yes.  That’s just why I wanted those names Dick heard.  They are likely to appear in any message that was sent.  So, if we can find words that correspond in length to those, we may be able to work it out.  Here goes, anyhow!”

For a long time Harry puzzled over the message.  He transcribed the Morse symbols first into English letters and found they made a hopeless and confused jumble, as he had expected.  The key to the letter E was useless, as he had also expected.  But finally, by making himself think in German, he began to see a light ahead.  And after an hour’s hard work he gave a cry of exultation.

“I believe I’ve got it!” he cried.  “Listen and see if this doesn’t sound reasonable!”

“Go ahead!” said Jack and Dick, eagerly.

“Here it is,” said Harry.  “Petrol just arranged.  Supply on way.  Reach Bray Friday.  Von Wedel may come.  Red light markers arranged.  Ealing Houndsditch Buckingham Admiralty War Office.  Closing.”

They stared at him, mystified.

“I suppose it does make sense,” said Dick.  “But what on earth does it mean, Harry?

“Oh, can’t you see?” cried Harry.  “Von Wedel is a commander of some sort — that’s plain, isn’t it?  And he’s to carry out a raid, destroying or attacking the places that are mentioned!  How can he do that?  He can’t be a naval commander.  He can’t be going to lead troops, because we know they can’t land.  Then how can he get here?  And why should he need petrol?”

They stared at him blankly.  Then, suddenly, Dick understood.

“He’ll come through the air!” he cried.

“Yes, in one of their big Zeppelins!” said Harry.  “I suppose she has been cruising off the coast.  She’s served as a wireless relay station, too.  The plant here at Bray Park could reach her, and she could relay the message on across the North Sea, to Helgoland or Wilhelmshaven.  She’s waited until everything was ready.”

“That what they mean by the red light markers, then?”

“Yes.  They could be on the roofs of houses, and masked, so that they wouldn’t be seen except from overhead.  They’d be in certain fixed positions, and the men on the Zeppelins would be able to calculate their aim, and drop their bombs so many degrees to the left or right of the red marking lights.”

“But we’ve got aeroplanes flying about, haven’t we?” said Jack.  “Wouldn’t they see those lights and wonder about them?”

“Yes, if they were showing all the time.  But you can depend on it that these Germans have provided for all that.  They will have arranged for the Zeppelin to be above the position, as near as they can guess them, at certain times — and the lights will only be shown at those times, and then only for a few seconds.  Even if someone else sees them, you see, there won’t be time to do anything.”

“You must be right, Harry!” said Jack, nervously.  “There’s no other way to explain that message.  How are we going to stop them?”