even know several Terrestrials who own Krovenkas."
"True enough," Jim conceded. "Nevertheless I have strong reasons for believing that this particular Krovenka came here direct from Mars. Do you see this chunk of clay? I dug it up from the place where the soil was pressed down by the flyer's landing gear. What do you make of it?"
Mayer examined the dirt, shook his head and said: "I'm afraid it doesn't mean a thing to me. What do you make of it," Jim?"
"Notice these purple specks?" Sullivan said, pointing to the clod.
Dan nodded.
"Now feel them."
Mayer did as he was bid.
"Ouch!" he yelled. "They're like tiny splinters of glass."
"Precisely," Jim grinned. "It's a sand composed of eroded, basaltic rock. Observe the peculiar, purplish color. To me that spells Zurek."
"I don't get you yet," Mayer confessed.
"I know of only one place where sand like that is found, and that is in the Martian Desert of Menfol. Of course I haven't explored every remote corner of the solar system, but I have visited most of the spaceports. The only one I know of where purple, vitreous sand like this is found is at Menfol. You know of course that the knave's roost which Zurek presides over is located there."
"But how do you account for the presence of the purple sand in this chunk of mud?"
"Don't you understand? When Zurek took off from Menfol, some of the sharp particles stuck to his landing gear. The place where he grounded on Ganymede has a heavy clayey soil to which the sand adhered. That proves pretty plainly that the flyer came from Menfol."
"Granted. But even that doesn't positively implicate Zurek."
"Maybe not, but, combined with these other clues it does." He pointed to the fragment of paper and the twisted wire."
"Better elucidate," Dan grinned. "I never was any good at solving puzzles."
"This," Sullivan explained, "is a piece of the wrapper from a package of vorgot. It's a rare drug which is mixed with a substance resembling chicle and is chewed like chewing gum. I happen to know that Zurek is a vorgot addict."
Picking up the wire he added: "This thing-a-goop cinches it. Ever see one before?"
Dan shook his head.
"It's a beard clip," Sullivan told him. "Zurek takes great pride in his whiskers, you know. He plaits them very artistically. To keep them from unraveling, he clips the ends in place with jiggers like this."
He waited an instant to let this sink in, then he went on: "Individually, of course, none of these clues prove much, but when they are all integrated the answer is Zurek."
By this time, Captain Brink had gained enough altitude so that he could take his attention away from the controls for a while.
"Hey, Jim," he called. "If you're through with your lecture on how to become a great cosmic sleuth in six easy lessons, suppose you call the Colonel and turn in a preliminary report of the massacre."
"O.K., Chief!"
Sullivan adjusted a dial on his short distance visaphone, a small, flat object shaped like a cigarette case which was fastened to the straps of his
