“Then what are they doing? Why are they digging that hole?” “They are looking for a souvenir.” “Eh? Are you jollying, Merry? A souvenir of what?” “Capt. Kidd!” The others had been listening eagerly. Frank’s words caused all of them to gasp for breath. “Then--then you think they are digging for----” “Kidd’s gold!” finished Merriwell. There was a moment of silence, and then Browning hoarsely whispered: “That’s it--just it! It explains everything.” “Everything but the prisoner. One of those four men is not here of his own free will. That is certain.” “And the mystery of the girl on board the vessel,” came from Harry. “It is certain she is not there of her own free will.” There was no doubt in the minds of the boys; all were satisfied that Frank had hit upon the truth. Harry, however, was no less afraid, for he realized that, without doubt, the men who had taken such pains to come there under cover of the storm and had brought a captive with them were ruffians capable of any desperate deed. The men worked steadily. One would use the pick a short time, and then the other would toss out the dirt with the spade. Not one of the four spoke. Deeper and deeper grew the hole. The light fell on the faces of the men occasionally. They were rough and bearded. Frank watched them closely, and he soon decided that one was the man who had been at the wheel of the black schooner when they first saw the vessel that day. Now there was no longer a doubt that the same black schooner lay in the cove, having run in there under cover of darkness, for all of the frightful risk. The boys had heard one of the men speak to Capt. Horn as they crouched to let them pass, and that was quite enough to settle the point. Who was Capt. Horn? He was the commander of the black schooner _Pirate_, but what was his record and his business? He had looked like a man who would not hesitate to enter into anything by which it seemed likely he might make money, no matter how dishonest or dangerous the project might be. Frank crept a bit nearer the four men, hugging the ground. The others followed him. Merriwell remembered the stories he had heard of other attempts to recover Kidd’s buried treasure--remembered how it had been necessary, according to superstition, for the treasure hunters to obey certain rules. They always dug on a dark and stormy night, and not one of the party could speak from the time they began to work till the treasure was found. If they did speak the treasure would turn to old iron or vanish entirely. For some time the boys watched the digging, wondering if there was a bare possibility that, at last, some one had located the spot where the pirate’s treasure was buried. The hole grew deeper and deeper. The two men got down into it, and were hidden to their hips. Frank became tired. He resolved to test the courage of the diggers in some manner.