Almost instantly Willie replied to the signal.
"Any message for us from Oakdale?" inquired Charley.
"Not a word. What are you doing?"
"We are investigating the cause of the fire. Have moved our aerial down past the burned area. Forester and Lew and I alone. Fire crew on way back to Oakdale."
"Have you found cause of fire?"
"No. Just got here. Haven't investigated yet. Will listen in every quarter hour, beginning with the hour."
"All right. I'll be here. Good-bye."
The minute Charley finished talking with Willie, the three investigators set about their work.
"We'll walk along the edge of the burned area," said the forester, "and try to find the point of origin."
He went ahead, the two boys following. They were facing toward the brook. The line was irregular, like a huge saw-blade, with little jutting, black teeth here and there, where the flames had crept out in advance of the main line. The wind that had come up when the boys were fighting the fire had driven the flames back upon the area they had already consumed and the blaze had died out of itself. It could not eat its way to windward out here in the open, as it could have done in the dense timber where the wind was broken. From their starting-point they walked to the brook, finding nothing to enlighten them. They then retraced their steps, walking along the windward edge of the fire. Yet they found nothing to show them how or where the fire originated.