He came to the chamber and there discovered us lying on the ground, overcome. He bent down and, to his great satisfaction, saw that we were really unconscious.

Quickly he moved over to the safe and pried open the last thin steel plate.

Inside was a small box. He picked it up and tried to open it, but it was locked. There was no time to work over it here, and he took it under his arm and started to leave.

He paused a moment to look at us, then took out a piece of paper and a pencil and on the paper wrote, "Thanks for your trouble." Beneath, it was signed by his special stamp--the serpent's head, mouth open and fangs showing.

Long Sin looked at us a moment, then a subtle smile seemed to spread over his face. At last he had us in his power.

He drew out a long, wicked-looking Chinese knife and stuck it through the note.

Then he felt the edge of the knife. It was keen.

In the sitting-room, Elaine, Aunt Tabby and Joshua had been listening intently at the fireplace but heard nothing.

They were now getting decidedly worried. Finally, the fumes which we had released made their way to the room. They were considerably diluted by fresh air by that time, but, although they were nauseous, were not sufficient to overcome any one. Still, the smell was terrible.

"I can't stand it any longer," cried Elaine. "I'm going down there to see what has become of them."

Aunt Tabby and Joshua tried to stop her, but she broke away from them and went down the ladder. Rusty leaped down after her.

Joshua tried to follow, but Aunt Tabby held him back. He would have gone, too, if she had not managed to strike the spring and shut the door, closing up the pa.s.sageway.

Joshua got angry then. "You are making a coward of me," he cried, beating on the panel with the b.u.t.t of his gun and struggling to open it.

He seemed unable to fathom the secret.

Elaine was now making her way as rapidly as she could through the tunnel, with Rusty beside her.

It was just as Long Sin had raised his knife that the sound of her footsteps alarmed him.

He paused and leaped to his feet.

There was no time for either to retreat. He started toward Elaine, and seized her roughly.

Back and forth over the rocky floor they struggled. As they fought,--she with frantic strength, he craftily,--he backed her slowly up against the prop that upheld the roof.

He raised his keen knife.

She recoiled. The prop, none too strong, suddenly gave way under her weight.

The whole roof of the chamber fell with a crash, earth and stone overwhelming Elaine and her a.s.sailant.

By this time Joshua had left the house and had gone out into the garden to get something to pry open the fireplace door.

Of a sudden, to his utter amazement, a few feet from him, it seemed as if the very earth sank in his garden, leaving a yawning chasm.

He looked, unable to make it out.

Before his very eyes a strange figure, the figure of Long Sin in his oxygen helmet, appeared, struggling up, as if by magic from the very earth, shaking the debris off himself, as a dog would shake off the water after a plunge in a pond.

Long Sin was gone in a moment.

Then again the earth began to move. A paw appeared, then a sharp black nose, and a moment later, Rusty, too, dug himself out.

Joshua had run into the house to get a spade when Rusty, like a shot, bolted for the house, took the window at a leap and all covered with earth landed before Joshua and Aunt Tabby.

"See!--he went down there--now he's here!" cried Aunt Tabby, pointing at the fireplace, then looking at the window.

Rusty was running back and forth from Joshua to the window.

"Follow him!" cried Aunt Tabby.

Rusty led the way back again to the garden, to the cave-in.

"Elaine!" gasped Aunt Tabby.

By this time Joshua was digging furiously. Rusty, too, seemed to understand. He threw back the earth with his paws, helping with every ounce of strength in his little body.

At last the spade turned up a bit of cloth.

"Elaine!" Aunt Tabby cried out again.

She was in a sort of little pocket, protected by the fortunate formation of the earth as it fell, yet almost suffocated, weak but conscious.

Aunt Tabby rushed up as Joshua laid down the spade and lifted out Elaine.

They were about to carry her into the house, when she cried weakly, but with all her remaining strength.

"No--no--Dig! Craig--Walter!" she managed to gasp.

Rusty, too, was still at it. Joshua fell to again. Man and dog worked with a will.

"There they are!" cried Elaine, as all three pulled us out, unconscious but still alive.

Though we did not know it, they carried us into the house, while Elaine and Aunt Tabby bustled about to get something to revive us.

At last I opened my eyes and saw the motherly Aunt Tabby bending over me. Craig was already revived, weak but ready now to do anything Elaine ordered, as she held his hand and stroked his forehead softly.

Meanwhile Long Sin had made his way to the automobile where his master, Wu, waited impatiently.