“No. I can’t find him anywhere.”

“Good God! Then I know what he has done,” said Masters brokenly. “He was very upset over Mrs. Desmond yesterday. She wanted me to open the shutters. Come.”

At the stern of the ship and on the lower deck was a little trap door in the metal covering. “He’s gone through there,” said Masters hoarsely. “He asked me a lot of questions about it last night. I told him about the mechanism of this trap and he suggested we should go out on deck, and see if it was possible to breathe out there. I laughed at him and thought no more about the matter.”

As he was speaking he deftly wound a scarf about his nose and mouth, and stuffed his ears with cotton wool saturated with oil. He touched a spring and a sheet of metal unfolded and when it rested at last in position, it formed a tiny air tight closet outside the trap. “I shall open the trap as quickly as I can,” said he quickly. “On the other side the deck is opened up and there is a space left large enough to test thoroughly the outer air. But by the aid of this “cubby-hole” we still have our ether protection kept safe all round the ship. Now I am going out to see if Murdoch is there. If I don’t come back, don’t search for me. It will be too late.”

“Masters, don’t go!” urged Alan.

“I must go,” grimly, “but I beg of you, if I don’t return in ten minutes, forget I ever existed.”

Without another word he slipped into the little boxlike chamber, and the door snapped to after him. They heard the sound of a click, rushing air, and then, silence.

Five minutes passed—six—seven—eight. Sir John, Desmond and Mavis had come up in time to hear the trap close, and quickly Alan explained the position.

“Why did you let him go?” cried Mavis.

“Murdoch went for you, my dear,” he answered sternly. “Masters went to save him.”