When Eph made the mooring cable fast, this shore boat ranged alongside.

“Box for Captain Benson, sah,” called the negro.

“Right here,” acknowledged Jack, going over to the rail.  The box proved to be of pasteboard.

“Are you going to open it?” whispered Farnum.

“Why, yes, sir; of course,” Jack answered.

“Better do it on deck, then,” came the dry answer.  “It might contain something explosive, you know.”

Though he laughed, young Benson carefully untied the string that held the lid on, also carefully removing the latter.  Inside he discovered a handsome bouquet of roses, with a card attached.

“Well, of all the assurance in the world?” gasped Jack Benson.

“What’s the matter!” queried Farnum.

“Read what’s written on this card, sir.”

The inscription ran: 

“Mlle. Sara Nadiboff is delighted at learning that Captain Jack Benson has returned in safety from his long walk.”

“Any answer, sah?” demanded the darkey in the boat.

“None, thank you,” replied Captain Jack, in an even tone.

The boat continued on its way to the shore.

“Say, what do you think of that?” demanded Eph, after he, too, had taken a look at the card tied to the flowers.

“It is plain enough that our charming young Russian doesn’t mean to drop Captain Benson’s acquaintance just yet, if she can help it,” laughed the shipbuilder.

“What are you going to do with the flowers, old man?” asked Hal.

“Flowers should be put in water, to make them keep, shouldn’t they” queried the young submarine skipper, innocently.

“Yep,” nodded Eph Somers.

“I hope these will keep fresh a long time, then,” murmured Benson.

Raising the bouquet he dropped it overboard the harbor—­on the side of the boat away from the hotel.

CHAPTER XV

CAPTAIN JACK BECOMES SUSPICIOUS

So successful and enjoyable a trip did the naval officers have that, as the “Benson” was gliding back to the harbor, Lieutenant Commander Kimball broached a subject that had begun to interest the society people among the winter visitors to Spruce Beach.

“Mr. Farnum,” inquired the naval officer, “I have a favor to ask of you.”

“You know in advance, Mr. Kimball, that it is granted.”

“I hope it is, if it’s a wise favor to ask,” smiled the naval officer.  “In brief, the idea is this:  Naturally people in this neighborhood are all agog over this submarine craft.  Some of the more daring of the ladies have besought me to arrange for a few of them to have a trip on board, even to running beneath the surface.  Will you do that, for a party of our friends, to-morrow afternoon?”

“We’ve been a good deal beset by spies lately as you have means of knowing,” replied Mr. Farnum, slowly.  “You’ll guarantee all of the guests, of course.”