“Where have you been so long?” inquired Mr. Lewis, his face not a little serious.

“We thought maybe something held you back,” added Dr. Kirshner.

“It did,” replied Bob, trying to remain calm.

The men sat up quickly, sensing that some misfortune had come upon the boys.

“What was it?” demanded Mr. Holton tensely.

“An army,” Joe returned soberly.

For a second there was silence. Then the men broke out in laughter. Evidently they thought the youths were joking. Even Fekmah joined in, his dark features drawn together in mirth.

“Nothing to laugh at,” said Joe, vexed because the men thought their experience funny. “It nearly scared Bob and me out of our wits.”

Mr. Holton grew more serious.

“Come, now,” he said. “Tell us what you mean.”