As he advanced cautiously, step by step, up the incline that led to daylight and the outer world, he felt at first a sense of disappointment when he saw no one with whom he might come to grips. He had been treated so meanly that it would have been a source of satisfaction to have had it out in a rough-and-tumble fight with those responsible. But, to his surprise, Tom pushed his way out through a tangle of underbrush and bushes which grew about this end of the tunnel and found none to dispute him. This surprise was added to when he looked about him and found out where he was. “On Barn Door Island!” exclaimed Tom. “Of all places! Barn Door Island! But how did I get here? It’s miles away from where I went down those steps near our plant. Of all places! Barn Door Island!” This was a small island in Lake Carlopa which had been named Barn Door because, some time or other, one of the early settlers happened to remark that it was no larger than the door of a barn. The island was at the end of the lake farthest removed from Shopton and the Swift plant. “I never knew there was an entrance to a tunnel here!” said Tom, as he looked about him. “But then I’ve never explored here very much.” Nor had any of the other lads of Shopton. Barn Door Island was a barren place—merely a collection of scrubby trees and tangled bushes and great boulders set down at the swampy end of Lake Carlopa. It was not a good fishing location and too dreary for picnic parties, so Barn Door was seldom visited. “But if I had an idea there was a tunnel entrance here—the beginning of a passage that led under the lake and under the land right up to our place I’d have done a lot of exploring, that’s sure!” Tom told himself. “That’s a natural tunnel, I’m positive of it, at least most of it is. Somebody went along it until they got to the end near our fence. Then they broke out, put in those steps and made the plank covering for the opening. They put earth over the planks so no one would see them. That part must have been done recently, for we were trying airships out in that field a month ago and I landed right near that bush behind which the man disappeared. I know I did, for I remember thinking I might crash into the fence. So the land end of this queer tunnel has only been opened lately. This island end must have been here a long while. But it’s queer no one knew of it. And I wonder what it’s being used for? Something to do with our business, I’m sure. Our enemies are at work again!” Tom quickly reviewed the situation in his mind. Since his Chest of Secrets had been taken and he had had so much trouble in recovering it, he had been very cautious about his plans of new inventions. Suspecting several of his newer employes, he had gotten rid of them and had taken great precautions, on the advice of Ned and his father.