“But, anyway,” insisted John Rhinds, blandly, “you must admit, Captain, that our possession of the full number of torpedoes allowed us is proof positive that we haven’t been firing even one of them.”

“That showing is certainly in your favor, Mr. Rhinds,” admitted the president of the naval board, coldly.  “I cannot see that the evidence at present available allows of my ordering anyone under arrest.  I am bound, in view of the fact that suspicion has pointed your way, to state that I intend to leave the corporal and four of the marine privates aboard.  On the home cruise a marine sentry will be posted, all the time, close to the after port of your torpedo tube.”

“It is humiliating—­very,” sighed Mr. Rhinds.  “Still, I shall be the last to offer any objection to any arrangement that seems wise to the members of the naval board.”

The corporal and four of his marines were therefore left under command of Ensign Pike, with instructions to see to it that constant guard was kept by the torpedo tube.

No allusion to the evidence could be made before the members of the cutter’s crew on the way back.  Captain Magowan led his own party to the office of the commander of the gunboat.

“Er—­gentlemen—­” began Magowan, slowly, “I must admit that our most elaborate case of circumstantial evidence seems to be knocked into a cocked hat by the one substantial fact that the ‘Thor’ still has her full number of torpedoes on board.”

“Then you don’t believe that torpedo came from the ‘Thor’s’ tube, Captain?” asked Jack Benson.

“I don’t know what I believe,” confessed the president of the board, shaking his head.  “It seems to be clearly established that no other submarine was near enough to have fired a torpedo to cover the range I have just been informed by Commander Ellis that the recovered torpedo has been examined, and has proved to have contained the full war charge.  More as a matter of form than anything else we will now order the remaining submarine boats alongside, and have them searched for a missing torpedo.”

That search was accordingly made, but not one of the boats had a torpedo less than the four that it was supposed to carry.

The object of the lightning cruise having been accomplished, in the destruction of the half-sunken derelict, the order was given to sail back to Groton Bay at less speed than had been used on the outward trip.

As far as evidence went the mystery of the attempt to destroy the “Hastings” appeared to be as big a mystery as ever.

CHAPTER XIX

ON THE OTHER SIDE OF THE FORCED DOOR

It was nearly dark, on the day following, when the submarine flotilla made its way up Groton Bay.

As soon as the craft was at its moorings the “Hastings” was immediately lighter by the going of one passenger.

Jacob Farnum went post-haste to the hospital, to inquire after David Pollard’s condition.