“What did he do?”

“Nothing much, except to stare in here as if he was sizing my place up.”

“Sizing it up?”

“Yes.  Getting the lay of the land, so he or some confederate could commit a robbery, maybe.”

“A robbery?  Do you think that man was a thief?”

“I don’t know that he was, Tom, and yet a jeweler has to be always on the watch, and that isn’t a joke, either, Tom Swift.  Swindlers and thieves are always on the alert for a chance to rob a jewelry store, and they work many games.”

“I didn’t notice any particular man looking in here,” said Tom, who still held the diamond brooch in his hand.

“Well I did,” went on the jeweler.  “I happened to glance out of the window when you were looking at the pins, and I saw his eyes staring in here in a suspicious manner.  He may have a confederate with him, and, when you’re gone, one may come in, and pretend to want to look at some diamonds.  Then, when I’m showing him some, the other man will enter, engage my attention, and the first man will slip out with a diamond ring or pin.  It’s often done.”

“You seem to have it all worked out, Mr. Track,” observed the lad, with a smile.  “How do you know but what I’m in with a gang of thieves, and that I’m only pretending to want to buy a diamond pin?”

“Oh, I guess I haven’t known you, Tom Swift, ever since you were big enough to toddle, not to be sure about what you’re up to.  But I certainly didn’t like the looks of that man.  However, let’s forget about him.  He seems to have gone down the street, and, after all, perhaps I was mistaken.  Just wait until I show you a few more styles before you decide.  The young lady may like one of these,” and the jeweler went to another showcase and took out some more trays of brooches.

“What makes you think she’s a young lady, Mr. Track?” asked the lad.

“Oh, it’s easy guessing, Tom.  We jewelers are good readers of character.  I can size up a young fellow coming in here to buy an engagement or a wedding ring, as soon as he enters the door.  I suppose you’ll soon be in the market for one of those, Tom, if all the reports I hear about you are true—­you and a certain Mary Nestor.”

“I—­er—­I think I don’t care for any of these pins,” spoke Tom, quickly, with a blush.  “I like the first lot best.  I think I’ll take the one I had in my hand when that man alarmed you.  Ha!  That’s odd!  What did I do with it?”

Tom looked about on the showcase, and glanced down on the floor.  He had mislaid the brooch, but the jeweler, with a laugh, lifted it out of a tray a moment later.

“I saw you lay it down,” he said.  “We jewelers have to be on the watch.  Here it is.  I’ll just put it in a box, and—­”

With an exclamation, Mr. Track gave a hasty glance toward his big show window.  Tom looked up, and saw a man’s face peering in.  At the sight of it, he, too, uttered a cry of surprise.