"It was the map they were after," thought Tom, "not my watch or money. This is more of the Foger's work. We must get away from here."
The policeman inquired for more particulars from Tom, who related how the hold-up had taken place. The young inventor, however, said nothing about the map he carried, letting the officer think it was an ordinary attempt at robbery, for Tom did not want any reference in the newspapers to his search for the valley of gold.
Presently the other policeman returned, having been unable to get any trace of the daring men. The two bluecoats wanted to accompany Tom back to the airship shed, for his own safety, but he declared there was no more danger, and, after having given his name, so that the affair might be reported at headquarters, he was allowed to go on his way. His head ached from the blow, but otherwise he was unhurt.
"Those fellows have been keeping watch for me," the lad reasoned, as he walked quickly toward the airship shed. "They must have been shadowing me, and they hid there until I came back. Andy Foger and his father must be getting desperate. I think I know why, too. That little dig I gave Andy about his map is bearing fruit. He begins to think it's the wrong map, and he wants to get hold of the right one. Well, they shan't if I can help it. We'll be away from here in the morning."
There was indignation and some alarm among Tom's friends when he told his story a little later that night.
"Bless my walking-stick!" cried Mr. Damon. "You'll need a bodyguard after this."
"I'd just like t' git my hands on them fellers!" exclaimed the old miner. "I'd show 'em!" and a look at his rugged frame and his muscular arms and gnarled hands showed Tom and Ned that in the event of a fight they could count much on Abe Abercrombie.
"I am glad there will be no more delays, and that we will soon be moving northward," spoke Mr. Parker, a little later. "I am anxious to confirm my theory about the advance of the ice crust, I met a man to-day who had just returned from the north of Alaska. He said that a severe winter had already set in up there. So I am anxious to get to the ice caves."
"So am I," added Tom, but it was for a different reason.
They were all up early the next morning, for there were several things to look after before they started on the trip that might bring much of danger to the adventurers. Under Tom's direction, more gas was generated, and forced into the big bag. A last adjustment was made of the planes, wing tips and rudders, and the motor was given a try-out.