The car came to a sudden stop. The Chief sprang to a fire-box and instantly in that room Johnny had so recently left a ticker sounded and a yellow light rose up and over. The second alarm had been sent.

Ten seconds later, on the wall of that strange room, two red spots and two white ones blinked out, then one that was half red and half white, and then a green one. At the same instant three fire engines, three truck and ladder companies and an emergency squad made the night hideous with their clanging bells and screaming sirens. The second alarm had been heard. Reinforcements were on the way.

Johnny thrilled to it all. It was, he told himself, like a great battle; only instead of fighting fellow human beings, men were fighting the enemy of all—fire.

“Fire! Fire! Fire!” rang up and down the streets.

In Johnny’s whirling brain one fact remained fixed; this fire had been set. By whom? How? These were the questions he had pledged to answer.

To Johnny, battle with a fire was always fascinating and inspiring. He knew well enough how this one would be waged. The enemy was within, and must be rushed, beaten back, defeated. There were three entrances. These would be stormed with men and water. There was a great central stairway to the very top of the six story building. The fire, if freed from the room in which it had its origin, would go leaping and laughing up those stairs. The top of the building must be reached at once. The poisonous fumes of the fire must be freed there and its flames beaten back. The roof might be reached from the fire escape. Already a line of rubber-coated men were toiling upward.

Ah yes, it was all very fascinating, but Johnny had his part to do. How had the fire started, and where? This he must discover if possible. One more thing; if the fire had been set, was the firebug still about the place? It is a well known fact that these men frequently linger about the scene of the fire.

“If he’s here mingling with the throng could I recognize him?”

As Johnny asked himself this question, he realized that the answer must almost certainly be “No.” And yet there was a chance. An expression of the face, a movement of muscles, might give the man away.

“But first the fire,” Johnny exclaimed as, leaping from the car, he sprang for the already battered down door of the front entrance. Gripping a hose that was being slowly dragged forward by the line of plucky firemen, he struggled forward with the rest. Beating back smoke and flames, they battled their way forward against the red enemy who even now might be seen leaping madly up the stairs.