When Tom and Mary came out of the House on Wheels a little later he had made certain of what he had suspected a long time, that Mary Nestor was worth to him more than all else in the world.
When Tom and Mary arrived at the Winthrop house some time afterward, they found a message from the State Police, announcing that Cunningham and his gang had fairly run into the net spread about Dismal Mountain for them, and with the exception of a few unimportant men, all were captured.
When Floyd Barton, who had been lodged in jail, heard this news, brought to him by Ned who went back to the castle to look things over, the young man caved in and made a complete confession. He was more a tool of his rascally uncle than anything else, but his money had furnished working capital for the bandits.
Floyd had been particularly struck by Mary's charm and had conducted a rushing campaign to make her capitulate to him. For a time, she afterward confessed to Tom, she had been fascinated by him. But his true character was soon apparent.
Thus the mystery of Dismal Mountain was cleared up. A search of the castle revealed not only much loot, besides the valuable instruments, but also machinery for turning out more. It had been Cunningham's intention to set up the machinery he had hoped to have Tom Swift make for him in this same castle and go into the illegal instrument manufacturing business on a large scale. But with the rounding-up of the gang, all these plans came to an end.
It was also discovered that many of the weird and ghostlike manifestations seen on Dismal Mountain were caused by the Cunningham gang with the object of keeping people away. Only Tom Swift's whimsical decision to investigate the place brought the tricks to light.
"Well, I guess it's all settled," Tom announced to Ned one day, when they had been guests at the Winthrop home for some days after all the rascals were sent to prison.
"What's all settled?" Ned wanted to know.
"My wedding plans. Mary and I are going on our honeymoon in the House on Wheels."
"What did I tell you?" chuckled Ned. "I knew, as soon as you began to build it, that you'd use it for that."