“What for so much hurry?” he grumbled.  “Get to Key West by afternoon, anyhow.  Dave want plenty sleep.”

“You slept like a top for six hours last night!” declared Alec.

“No-o; Dave watch, saw steamer,—–­no more sleep, no forty winks.”

“Oh, come!” laughed Billy.  “I heard you snoring, Dave; you woke me up!  I thought it was thunder!”

“Nothing less than thunder or a cannon firecracker would wake you up, Billy,—–­as a general rule,” said Hugh, flinging one arm over his chum’s shoulders and giving him a vigorous hug.

“Look yonder, boys!” shouted Captain Vinton at the helm.  He pointed aft, and the four lads sprang to their feet and hurried toward him, alert and eager for a new surprise.

Some distance behind them, toward the mainland, a thin trail of smoke which had not been seen for two or three hours was now visible inside the keys.  Could there be any reason for the reappearance of that smoky blur against the sky?  Was it made by the mysterious steamer?  If so, was she following the Arrow?

“By the shades o’ shad, I orter know that boat!” exclaimed Vinton in puzzled chagrin.  “See?  She’s coaled up, goin’ for all she’s worth.  Alec, git out my glass from the cabin, take a look, and see if there’s many men aboard.”

Alec ran to do the captain’s bidding.  Descending into the cabin, he took from a locker an old-style marine telescope with which he hurriedly returned to the deck.  After some focusing he managed to catch a glimpse of the steamcraft, just before she partially disappeared from sight behind one of the sandy reefs that fence off the sound.

“The crew of the steamer seem to be quite excited,” Alec said, as he trained the telescope upon them.  “I can see sailors running across her deck, and two of them have just hoisted an American flag.  Some others are waving signals and—–­”

“What?” shouted the captain.  “American flag, did you say?”

“Yes.  What do you think of that?”

“Reckon she wants to speak us.”

“Why?” asked Chester.

“Looks like this is the first time she’s seen us,” said Vinton, taking the marine glass from Alec.  “But it can’t be the same craft we sighted back yonder, last night.  Anyhow, if they’re wavin’ signal flags,—–­and they are, sure enough!—–­they must want to speak the Arrow.  That’s plain.  I’m goin’ to ease in more and see who’s aboard.  Look! the dinged old boat is comin’ out from behind the bar now.”

Pondering some contingency which he did not explain to the boys, Vinton shifted the helm; and his sloop, hitherto heading in a southwesterly direction, now began to edge closer to the line of keys.  Had Vinton not known his course so thoroughly from long experience in sailing these channels, inlets, and lagoons, it would have been dangerous; but he dexterously eluded the various reefs and oyster bars and brought the Arrow safely into smoother water.  Meanwhile, the boys noticed that the wind, which had blown so strongly, was beginning to slacken, thus allowing the steamer to gain on the Arrow quite perceptibly.  They saw then that she was a small steamer, like a steam yacht, and light gray in color,—–­perhaps one of the United States revenue cutters.