“A call to battle!” murmured Joe.

“Actual fighting?” added his chum wonderingly.

“Perhaps I’d better explain a bit,” went on the film producer.  “Most unexpectedly there has come to me an opportunity to get some exceptional pictures.  I need resourceful, nervy operators to act as camera men, and it is only paying you two a deserved compliment when I say I at once thought of you.”

“Thank you,” murmured Blake.

“No thanks necessary,” responded Mr. Hadley.

“So now I am ready to put my offer into words.  In brief, it is——­”

At that moment back of the farmhouse (which was partly in ruins, for the fire had been a real one) a loud explosion sounded.  This was followed by shouts and yells.

“Somebody’s hurt!” cried Mr. Hadley, and he set off on a run toward the scene, followed by Blake and Joe.

And while they are investigating what had happened, advantage will be taken of the opportunity to tell new readers something of the former books in this series, so they may feel better acquainted with the two young men who are to pose as “heroes,” as it is conventionally termed, though, in truth, Joe and Blake would resent that word.

“The Moving Picture Boys” is the title of the first volume of the series, and in that the readers were introduced to Blake Stewart and Joe Duncan while they were working on adjoining farms.  A moving picture company came to the fields to make certain scenes and, eventually, the two young men made the acquaintance of the manager, Mr. Hadley.

Blake and Joe were eager to get into the film business, and their wish was gratified.  They went to New York, learned the ins and outs of the making of “shifting scenes,” as the Scotchman called them, and they had many adventures.  The boys became favorites with the picture players, among whom were the gloomy C. C., Miss Shay, Miss Lee, Harris Levinberg and Henry Robertson.  Others were added from time to time, sometimes many extra men and women being engaged, in, for instance, scenes like these of “The Dividing Line.”

Following their adventures in New York, which were varied and strenuous, the moving picture boys went out West, taking scenes among the cowboys and Indians.

Later they moved on, with the theatrical company, to the coast, where they filmed a realistic picture of a wreck.  In the jungle was where we next met Blake and Joe, and they were in dire peril more than once, photographing wild animals, though the dangers there were surpassed when they went to Earthquake Land, as they called it.  The details of their happenings there will be found in the fifth volume of the series.

Perilous days on the Mississippi followed, when Blake and Joe took pictures of the flood, and later they were sent to Panama to make views of the digging of the big canal.

Mr. Hadley was a producer who was always eager for new thrills and effects.  And when he thought he had exhausted those to be secured on the earth, he took to the ocean.  And in “The Moving Picture Boys Under the Sea,” the book that immediately precedes the present volume, will be found set down what happened to Blake and Joe when, in a submarine, they took views beneath the surface.