Followed by the sympathetic four, the old man hobbled up from his little wharf to a small eminence on which stood his neatly whitewashed hut.  He opened the door and invited them in.  A first glance discovered nothing much the matter, but a second look showed the boys poor old Skipper lying on the floor in front of the open fireplace which was filled with fresh green boughs—­ and evidently a very sick dog indeed.  He gave the boys a pathetic glance of recognition as they came in, and with a feeble wag or two of his tail tried to show them he was glad to see them; but this done, he seemed to be completely exhausted, and once more laid his head between his forepaws and seemed to doze.

“Poor old dog,” said the captain, shaking his head.  “I doubt if he’ll ever get about again.”

The safe now engaged the boys’ attention.  It is true that it was a rickety old contrivance which might well have been forced open with an, ordinary poker, but to the captain, up to this day, it had been a repository as safe and secure as a big Wall Street trust company’s vaults.

“Look at that, boys!” cried the captain, with tragic emphasis, pointing to the door, which had been forced clear off its rusty hinges.  “Just busted open like yer’d taken the crust off’n a pie!  Ah, if I could lay my hands on the fellers that done this, I’d run ’em tip ter the yardarm afore a foc’sle hand could say ’Hard tack’!”

“Why, we think that—­” began Tubby, when Rob checked him.  The captain, who had been bending over his dog, didn’t hear the remark, and Rob hastily whispered to Tubby: 

“Don’t breathe a word to anyone of our suspicions.  Our only chance to get hold of the real culprits is to not give them any idea that we suspect them.”

After a little more time spent on the island, the boys took their leave, promising to come back soon again.  First, however, Rob and his corporal made a brief expedition to see if they could make out the tracks of the marauders of the previous evening.  Whoever they had been, however—­and the boys, as we know, had a shrewd guess at their identity—­they had been too cunning to take the path, but had apparently, judging from the absence of all footmarks, made their way to the house through the coarse grass that grew on each side of the way.

“Well, what are we going to do about it?” Tubby inquired, as they speeded back toward home.

“Just what I said,” rejoined Rob.  “Keep quiet and not let Jack or his chums know that we suspect a thing.  Give them enough rope, and we’ll get them in time.  I’m certain of it.”

How true his words were to prove, Rob at that time little imagined, although he felt the wisdom of the course he had advised.

As they neared the inlet, Rob, who was at the wheel and scanning the channel pretty closely, for the tide was now running out, gave a sudden shout and pointed ahead.  As the others raised their eyes and gazed in the direction their leader indicated they, too, uttered a cry of astonishment.  From the mouth of the inlet there had stolen a long, low, black craft, gliding through the water at tremendous speed.