one volley. In other words the alley was a trap."

"By ginger, I believe you're right!" exclaimed Bart "The shots came just after the light was flashed. It was a slick trick. You have to hand it to them."

"But that doesn't explain where the men disappeared to who went into the alley first," remarked Billy.

"No," admitted Frank. "And it doesn't explain either where the men who fired the shots vanished to. But there's an answer to everything, and I'm going to try to find the answer to this. I'm not going to drop it. Of course, I suppose the secret service men will take the thing up, but I'm going to do a little investigating on my own account. I have a hunch that when I take a look at that alley by daylight, I'll tumble to something."

And while the four chums, after their narrow escape, are cudgeling their brains to solve the mystery, it may be well for the sake of those who have not read the preceding volumes of this series to trace briefly their adventures before this story opens.

Frank Sheldon, a vigorous, clean-cut, young fellow, was a resident of Camport, a thriving and prosperous town of about twenty-five thousand people. His father had died a few years before the war broke out, and Frank lived in a little cottage with his mother, of whom for some years he was the sole support. She was of French birth, and by the death of her father had recently come into possession of a considerable estate in France. There had been some legal complications regarding the settlement of the property, and she had intended to go to France to look after her interests when the outbreak of the war made this impossible.

Frank was employed in the wholesale hardware house of Moore and Thomas, and his prospects for the future were very bright when the United States entered the World War. Frank was above everything else a hundred-per-cent American, and if he had consulted only his own wishes would have enlisted at once. But his mother's dependence upon him made him hesitate. An episode occurred, however, that decided him, when he was forced to knock down a burly German who had insulted the American flag. There was no further opposition by his mother, and he joined the Thirty-seventh Regiment, a Camport regiment with a glorious record in the Civil War, and one which had recently seen service on the Mexican border.

Billy Waldon, a close friend of Frank, was already a member, and Bart Raymond, Frank's special chum and a fellow employee, joined also. Another friend, Tom Bradford, tried to join, but was rejected on account of his teeth. He was afterward accepted in the draft, however, so that the four chums, to their great joy, found themselves together in the same regiment.

There was one man in the Moore and Thomas firm who was a bitter and malignant anti-American from the start. His name was Nick Rabig, and he was foreman of one of the departments. He was born in America, but his parents were German. Rabig and Frank Sheldon were at sword's points most of the time because of the former's bullying disposition, and after Rabig had been caught in the draft and forced into the ranks of the old Thirty-seventh he got from Frank the thorough thrashing which had been for a long time coming to him.

What experiences the Army Boys went through in the training camps, how narrowly they escaped a submarine attack on the way to Europe, what exciting adventures they met with on their first contact with the enemy, are described in the first volume of the series entitled: "Army Boys in France; Or, From Training Camp to Trenches."

After they had once reached the scene of action the adventures of the Army Boys multiplied rapidly. Trench warfare was soon outgrown, and open fighting in the field became the order of the day. At one time when the American troops were advancing, the boys became separated from their comrades and were compelled to leap from a broken bridge into a stream, and when they attempted to