"Self-preservation is the first law of nature," said Kraag cynically. "Better that two should die than three. Come on in, Jonner." "That's self-preservation? No thanks, Kraag. You know I'll turn you in as a murderer when the rescue ship gets here. I have no hankering to walk up where you can burn me down." "Okay, stay out there till your air gives out." The airlock was not a comfortable place to spend one of the asteroid's seven-hour nights, but Kraag was afraid not to stand guard there with his heat-gun. He was afraid to sleep, too, for the airlock combination was virtually noiseless and Jonner could open it from the outside. Jonner was unarmed, but Kraag had no hankering for a hand-to-hand fight with the powerfully built captain inside the personnel sphere. Because the air would swish out of the lock instantly if Jonner opened it, Kraag had to wear a spacesuit. He tried to talk to Jonner several times, but got no answer. Toward dawn, Kraag dozed off, only to be brought awake with a start by Jonner's voice in his earphones. "Good morning, Kraag," said Jonner. There was iron in his voice. "Have a good night's sleep?" "About as good as yours, I'd say," retorted Kraag, wishing he could get his hands inside his helmet to rub his eyes. "I slept fine. Found me a good foxhole just beyond the horizon." "Damn you, Jonner! Where are you now?" "Go on and have breakfast, Kraag. I'm far enough away for you to see me. Take a look." Kraag peered out of the uppermost airlock ports, one by one. They slanted at a bad angle, but through one of them he made out Jonner, standing half a mile away. Uncannily, as though he could see Kraag's helmet at the port, Jonner waved. Kraag was afraid to take off the spacesuit now because the supply deck had no ports and Jonner could get to the ship in a hurry if he wanted to. He took off the helmet, though, and went up to the center deck. Hurriedly, he opened the cover of the port in the direction he had seen Jonner. Jonner was still in the same place, sitting down. Kraag heated breakfast and ate it with an eye on the port. Jonner didn't move. Kraag felt better when he had eaten, and went up to the control room. "Why don't you give it up and come on in, Jonner?" he asked. "The oxygen in that suit's not good for more than another 15 hours." "That's where you're wrong, Kraag, and that's what's so tragic about your murdering Stein," said Jonner quietly. "You either forgot that we carried oxygen instead of nitric acid as the fuel oxidizer this trip or, being an engineer, you didn't think of it except as fuel. "There's enough oxygen in the tanks scattered over the landscape to keep a dozen men alive until the rescue ship gets here. It's hard for me to get at, but I've already found I can manage it." Kraag was profoundly shocked. For a moment the enormity of what he had done in killing Stein almost overwhelmed him. It had been completely unnecessary.