"Well, all right, but we shall have to be careful."
"Right you are," Frank agreed, "one little slip and the whole thing will be spoiled."
"Then there must be no slip," said Jack, quietly
"I agree with you there. Now the question arise? as how the thing may best be done."
"We'll have to wait until they're all asleep," said Jack.
"You forget the sentinels won't sleep," said Frank.
"No, I don't; and they will be the first disposed of. They are not looking for enemies from within, you know. You walk up to one and I'll walk up to the other. We'll be challenged when we get close, of course. Then it will be up to us to silence those fellows before they can make an outcry."
"We'll try it. Then what?"
"Then we'll come back and put the airships out of commission as carefully as possible."
"That's easy enough. All we have to do is to let out the 'gas.'"