"But it is impossible to pierce such a wall as that," said Harry.

"We'll try, at all events," Jack responded. "Come, boys," he added, "one last desperate effort, and we'll baffle 'em yet."

The waiter and diver understood in a minute.

Hurriedly they collected the tools--pickaxes, crowbars, chisels, and hammers--and they all set to work on the masonry.

But their momentary hopes soon subsided.

The mortar had, in the course of ages, become even harder than the stone itself.

It was impossible to make any impression upon it.

When they saw this, disappointment was depicted upon every countenance.

Jack flung down, in sheer despair, the chisel with which he had attempted to break the mortar.

As the implement fell upon the stones of the courtyard, Thyra's quick ear noticed the peculiar sound.

"It is hollow beneath here," she exclaimed, eagerly.

Again testing the floor in the same way, they became convinced that she was right.

There were probably vaults beneath this courtyard, and this stone concealed the entrance to them.

Animated by this fresh hope, the party now worked away, and in a few minutes had lifted the ponderous flagstone.

A flight of rude steps, leading down into utter darkness, was discovered.

"As I thought," cried Jack, "these are vaults; we may baffle them after all. Bogey, run down immediately and see what they are like."

Bogey hesitated not a moment, but skipped down the rude steps and disappeared.

The others waited his return with great anxiety.

At this moment, a shout of triumph was raised by their enemies outside.

It signified that the cannon had been brought, and that the attack would soon recommence.

The hope of escape was still of the very slightest.

In a few moments Bogey returned.

"Well?" asked Jack.

"All cellars, ma.s.sa, goin' along--oh, miles and miles under de earth, all dark, 'cepting a bit of light that comes here and there through little holes in de roof. Plenty of room to hide all of us, sar. Oh, golly, won't de nasty Turks go mad?"

"Hurrah! down you go immediately," said Jack. "Now then, ladies first.

Harry, I commend Thyra to your care. Take her down."

"I can not, will not leave you, dear Jack," she cried, desperately clinging to our hero.

"No, no; I will soon be with you. For Heaven's sake. Thyra, do not hesitate now, or we shall all be lost. Go quietly; it is my wish."

Thyra resisted no more, but with Harry's a.s.sistance descended the steps into the vault.

"Now, Mr. Mole, down you go," said Jack. "Here, Figgins, you take his legs and go first, or they'll be running away with him again. Tinker, follow behind, supporting his head."

But Mr. Mole objected to this arrangement.

"What! do you think I'm an infant, to need carrying?" he said, with offended dignity. "No, though I have got patent self-controlling cork legs, I can walk down by myself."

And to prove this, he began jauntily descending the steps.

But the next moment he lost his footing, and with a cry, tumbled right down to the bottom, on to the body of the unfortunate orphan.

Luckily, it was not very far to fall, and Mr. Mole was very little hurt, though Figgins got the worst of it.

"Now, boys, down you go," cried Jack. "Hark! they are battering down the gate with artillery."

At that moment a ball tore through the doorway, shattered the top of the barricade, and at length lodged in the solid masonry.

Yells of triumph broke from the Turks.

"Quick! Tinker, Bogey, for your lives!" cried Jack.

"Is it that we are to desart ye!" cried the Irish diver. "No, Mr. Jack, I'll see you down first."

"Please make haste," said Jack almost imploringly. "Of course I shall save myself; but I'm the captain, you know, and I mustn't leave the ship till the last."

Thus rea.s.sured, the rest descended, and no sooner was the last safe in the vault, than Jack Harkaway shut down the stone in its place, thus closing the opening.

Then he hastily laid earth in the interstices round it, and tried to efface all signs of its having been recently removed.

With equal rapidity, he gathered up the crowbars, chisels, etc.

All this time the firing continued.

The door would soon give way and the enemy pour into the courtyard.

Was our hero mad, thus to remain behind while his friends escaped?

No.

His conduct was part of a desperate and deep-laid design.

He saw that if he had followed them in their rapid flight, the Turks would be sure to perceive that the stone had been removed, and this would at once enable them to discover the retreat of the whole party.

By remaining outside, he could restore the stone to its original appearance.