“My bet is nitroglycerine—–­what the bank robbers call ‘soup,’” declared Hemingway, almost in a whisper.  “All right; we’ll take it up to the station house.  Then we’ll send for Dr. Thornton, who is the best chemist hereabouts.  As soon as we get this stuff to the station house I’ll hustle back and hide against the coming of Mr. Tripps.  If he comes before I get back, jump on the fellow and hold him for me, no matter what kind of a fight he puts up.”

Dave gazed after the retreating figures of the policemen.

“Bright man, that Hemingway,” he remarked.  “If Tripps shows up, we are to jump on him and nail him—–­no matter if he hauls out two six-shooter and turns ’em on us”

“We can grab any one man, and hold him,” returned Dick, confidently.  “All we’ve got to do is to get at him from all sides.  See here, Dave, if a fellow comes in and tells you he’s Tripps, you repeat the name as though you weren’t sure.  As soon as we hear the name, Tom and I can jump on him from behind, and you can sail in in front.  Eh, Reade?”

“It sounds good,” nodded Tom.  “I’ll take a chance on it, Dick, with you to engineer the job.”

In ten minutes Officer Hemingway was back.  He stepped into a cupboard close to the counter, prepared for the coming of Tripps.

Half an hour later the police station’s officer in charge telephoned that Dr. Thornton had carefully opened the box, and had declared that it contained four pounds of nitroglycerine.  Nor had Dr. Thornton taken any chances of mistake.  He had taken a minute quantity of the suspected stuff out in the yard back of the station house, and had exploded it.

At a moment when the office was empty of patrons Mr. Drowan stepped into the cupboard for a moment, as though searching for something.

“How late do you stay open?” whispered Hemingway.

“Ten o’clock, usually, on Saturday nights, but we’ll keep open as late as you want, officer.”

“Better keep open until midnight, then.”

So they did, Dick telephoning his parents at the store to explain that he was at the express office helping Dave.

Midnight came and went.  A few minutes after the new day had begun Hemingway came out of the cupboard.

“You may as well close up, Drowan,” the plain clothes man decided.  “The fellow who calls himself Tripps isn’t going to show up.  If he had been going to claim his box he’d have been here before this.”

“You think he got scared away?” asked the night manager.

“The fellow was probably keeping watch on this office.  He saw what happened, and decided not to run his neck into a noose.  You’ll never have any word from Tripps.”

“Isn’t it just barely possible,” hinted one of the clerks, “that the man wanted the stuff for some legitimate purpose?”

“A man who knows how to use nitroglycerine,” retorted Hemingway, gruffly, “also knows that it’s against the law to ship nitroglycerine unlabeled.  He also knows that it’s against the law for an express company to transport the stuff on a car that is part of a passenger train.  So this fellow who calls himself Tripps is a crook.  We haven’t caught him, but we’ve stopped him from using his ‘soup’ the way he had intended to use it.”