"Well, if Mark came here he's not here now," thought Jack, "and there's no use in my staying any longer. Maybe something happened that he had to go back home. Perhaps he's trailing the man. We should have made up some plan to be followed in case anything like that happened." Deciding that the best thing he could do would be to go back home Jack came out of the old house. As he did so he gave a final call: "Mark! Oh, you Mark! Are you anywhere about?" What was that? Was it an answer, or merely the echo of his own voice? Jack started, and then, as he heard another sound, he said: "Only the wind squeaking a shutter. Mark isn't here." If Jack had only known! Through the quickly-gathering darkness Jack turned his steps toward home. On the way along the country road he kept a sharp lookout for any sign of his chum, and, also, he looked to see if he could catch a glimpse of any person who might answer the description of the man they suspected of tampering with the Cardite motor. But the road was deserted, save for an occasional farmer urging his horses along, that he might the more quickly get home to supper. "It's mighty strange," mused Jack, as he kept on. "I don't think Mark did just right, and yet, perhaps, when it's all explained, he may have good reasons for what he did. Maybe I'm wrong to worry about him, and, just as likely as not, he's safe home, wondering what kept me. But he might have known that I'd come back to the barn where I said I'd meet him. Of course that dog-fight delayed me a little, but not much." It was quite dark when Jack reached the house where he and his chum lived with the two professors. There was a cheerful light glowing from many windows, and Jack also noticed an illumination in the shed where the projectile was housed. "Guess they're working on it, to get it in shape for the trip, sooner than they expected," he mused. Jack was met at the door by Washington White. "Hello, Wash!" greeted the lad. "Good land a' massy! Where hab yo' been transmigatorying yo'se'f during de period when the conglomeration of carbohydrates and protoids hab been projected on to de interplanetary plane ob de rectangle?" "Do you mean where have I been while supper was getting ready?" asked Jack. "Dat's 'zackly what I means, Massa Jack." "Then why don't you say it?" "I done did. Dat's what I done. Supper's cold. But where am Massa Mark?" "What! Isn't Mark home?" cried Jack, starting back in alarm. "No, Massa Jack, we ain't seed him sence yo' two went off togedder. Where yo' all been?" "Mark not home!" gasped Mark. "Where is Professor Henderson, Wash? I must speak to him at once." "He am out in de shed wif Massa Roumann." With fear in his heart Jack dashed out toward the big shed. "Ain't yo' goin' t' hab some supper?" called Washington. "I don't want any supper--yet," flung back Jack over his shoulder. CHAPTER IX A DARING PLOT