He made a hasty search through the lower rooms, but saw no sign of Mark. It was the same upstairs, and on the third floor there was no evidence of his chum. Jack called again, but got no reply.
"The garret next, and then the cellar," he told himself, and these two places, darker and more dismal than any other parts of the old mansion, were soon explored.
"Well, if Mark came here he's not here now," thought Jack, "and there's no use in my staying any longer. Maybe something happened that he had to go back home. Perhaps he's trailing the man. We should have made up some plan to be followed in case anything like that happened."
Deciding that the best thing he could do would be to go back home Jack came out of the old house. As he did so he gave a final call:
"Mark! Oh, you Mark! Are you anywhere about?"
What was that? Was it an answer, or merely the echo of his own voice?
Jack started, and then, as he heard another sound, he said:
"Only the wind squeaking a shutter. Mark isn't here."
If Jack had only known!
Through the quickly-gathering darkness Jack turned his steps toward home. On the way along the country road he kept a sharp lookout for any sign of his chum, and, also, he looked to see if he could catch a glimpse of any person who might answer the description of the man they suspected of tampering with the Cardite motor.
But the road was deserted, save for an occasional farmer urging his horses along, that he might the more quickly get home to supper.