“What’s doing?  Have you found the gentleman’s notebook lying carelessly around, and which we can peep into, eh, Frank?”

“Not at all,” came the reply.  “I was only looking at this blotter.”

“Whatever is there funny about that?” demanded the other, in puzzled tones, as he glanced first at the object in question, and then up at the face of his chum.

“It was a new one, or nearly so, you see! and somebody has been writing heavily, and then pressing the blotter over it,” Frank went on.

“And if you could read backwards now, you might make out what they said; is that it, Frank?”

“Oh! that part is as easy as falling off a log.  I held it up to the looking glass here.  See if you can make it out, Andy.”

Hardly had the other looked than he started to read, interjecting remarks of his own as he proceeded.

“Some words missing, looks like, Frank; let’s see; ’Car on siding——­’rive at 11 P.M.  Wed.  He says keep low, and trust to him—­throw—­track.  Mum.’  That’s all I can make out, because he didn’t sign any name, it seems.  Whatever do you make of all that stuff, Frank?”

First of all Frank pulled out a pencil and copied the marks upon a piece of paper, which he thrust into his pocket.

“He might miss the blotter if I cribbed it, and take the alarm,” he explained, as he hastened to put the article in question back on the table, lest Sallie come in at any minute and discover what they were doing, taking liberties in the room of the boarder; and then she would have to be told everything, which might work out badly, Frank feared.

“But I reckon you’ve got some sort of idea what that writing means, Frank?” pursued the other Bird boy, who, once he started on a subject could no more be shaken off than a bulldog.

“Of course I have, and it’s given me something of a shock, too, let me tell you, Andy.  First of all, you may know that this very day is Wednesday.”

“The day he mentions there; to be sure it is.  But Frank, can all this have some reference to another crime they mean to commit?”

“I’m afraid it does,” came the reluctant reply.

“Tell me what he means by ‘car, siding, track, mum,’ and all that.  Of course I can understand that he warns the fellow he’s sending the message to to keep quiet.  What car can he mean?  Do you think they aim to steal some one’s expensive car now—­that they’ve gone and wrecked Percy’s biplane, and must have another means for getting away?”

But Frank simply shook his head at that.

“Oh! you’re away off your base there, Andy.  He speaks of a car on a siding, and that can only refer to a railroad car.  Now, I happen to know that they expect the pay-car to be along some time today or tonight, and it always lies there on that Jeffreys Siding, until they’ve passed out thousands of dollars to the men who call Bloomsbury their headquarters.  Do you see now what it must mean, Andy?”