lying there melting, absorbs the heat swiftly. So more heat is pumped into the room. Well, figure fifteen minutes before all the ice was liquified. More than enough of a margin of safety."

"Safety for whom?" Snow asked.

"For whoever didn't want Anders finding any evidence of how the disappearance was accomplished. About an hour passed between takeoff and the time he checked the cabin. You must remember that Anders had to maneuver the ship free of Mars' gravity, set his course for Earth, and then make a final check of all his equipment before going back into the ship proper. That takes plenty of time."

"But how could you figure this out?" Snow asked, her eyes wide with interest. "And where did the ice come from?"

"From the night side of Mars," I said. "Where the temperature drops below zero as soon as the sun has gone down. Remember, the ship was in a landing berth, and had just been prepared for a takeoff. The technicians would have moved away to be clear of the blast. In fact, they'd all be inside their shacks, having coffee against the chilly weather they'd been exposed to. All it took was someone bright enough to get hold of the water tank, and to spray the water into any handy container where it would freeze solid in a few seconds. Then the chunks of ice were substituted for the boys in the bunks, and Anders took off with no one but himself on board."

"You reasoned this out?" Snow said, incredulously. "How?"

"My gift for spotting, which I told you about. Once I knew that the boys could not have been kidnapped from space, and that something had to be making up for their mass aboard the Phobos II, I tried to think of where this something could be kept. It wasn't in the open, nor in any of the storage space. Therefore, it had to be within the bulkheads. But what could go within the bulkheads? Only water which had been taken from the air to keep the humidity down. And yet this water had to remain--without a container, mind you--in the fifteen racks at takeoff time so that Anders' dial would register them as all being securely in place before he pressed the starter. So in what form could water sit on a bunk without a container?"

Snow smiled helplessly, "Ice, of course. You make it sound almost idiotically simple." Then her face fell. "But it's only a theory, isn't it! Or is it?"

I shrugged. "It seems borne out by a few things, Snow. When I entered the Phobos, I 

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