"I'm afraid we'll have to leave them here," said Steve. "I wish there was some way for us to take them along, but I don't see how we can. We might be able to drag Hallo with us, but we wouldn't get very far."
"I suppose not. He has lots of friends, hasn't he? I saw ever so many people stop and speak to him when I was following him on the way here."
"I don't think he's got many friends, but there are a lot of people who know him, all right. Still, it isn't that—it would be making ourselves conspicuous by having him with us at all."
"It would be a good thing to take him, though, if we could, wouldn't it?"
"Oh, yes. The best thing in the world! If we could only get him to our boat and carry him back to Belgrade!"
"Steve, how about the men who are working in the tunnel under the arsenal?"
"What do you mean? What do you know about the tunnel under the arsenal?"
Steve was startled and dismayed, but Dick laughed at him.
"That's all I know," he said. "Just that there is such a thing, Steve. You needn't be frightened—I haven't been spying around. But this man that came here to see Mike Hallo knew all about it. He told him the mine was going to be sprung to-night, and that they must hasten to stop it."
"That ends the last doubt! He is a traitor!" said Steve. "He surely will have to pay the price of treachery, too, when there is an opportunity."