Had Ferguson and Metty actually come in to tap off a sample, as he had suggested to Willows? He looked around at the wreckage in the antechamber. Quite obviously, the heavy door of the sample chamber was wide open, and it certainly appeared that the wreckage was scattered from that point. Cautiously, he went over to look at the open sample chamber. It looked all right, except that the bottom was covered with a bright, metallic dust. He rubbed his finger over it and looked at the fingertip. A very fine dust. And yet it hadn't been scattered very much by the explosion. Heavy. Very likely osmium. Osmium 187 was stable, but it wasn't a normally used step toward Mercury 203. Four successive alpha captures would give Polonium 203, not mercury. Ditto for an oxygen fusion. It could be iridium or platinum, of course. Whatever it was, the instruments in his helmet told him it wasn't hot. He had a hunch that Ferguson and Metty had been building Mercury 203 from Hafnium 179 by the process of successive fusions with Hydrogen 3 and that something had gone wrong with the H-3 production. It appeared that the explosion had been a simple chemical blast caused by the air oxidation of H-2. But the bleeder vent at the other end of the reactor had apparently kicked at the same time. An enormous amount of unused energy had been released, blowing the entire emergency bleeder system out. Something didn't seem right. Something stuck in his craw, and he couldn't figure out what it was. He opened up the conduit boxes that led through the antechamber from the control console to the reactor beyond the firewall. Everything looked fine. That meant that whatever it was that had fouled up the controls was on the other side of the firewall. "How does it look?" Willows' voice came worriedly over the earphones. "Have I already said 'damn'?" de Hooch asked. "You have," Willows said with forced lightness. "You even said 'double damn'." "_Factorial_ damn, then!" said de Hooch. "What's the matter?" "Apparently the foul-up is on the _other_ side of the firewall." "Are you going in?" "I'll have to." "All right. Watch yourself." "I will." He went over to the periscope that surveyed the part of the reactor beyond the firewall. Everything looked normal enough. He carefully checked the pressure gauge. Normal. "Check the spectro for me, will you?" he asked. "Make sure that's just the normal helium atmosphere in there." "Sure." A pause. "Nothing but helium, Guz. What were you expecting?" "I don't think I'd care to walk into a hydrogen atmosphere at three hundred Centigrade." "Neither would I, but how could there be hydrogen in there?" "There shouldn't be. But there's something screwy going on here, and I can't put my finger on it." "Well, whatever it is, it isn't hydrogen in the reactor room." "O.K. Stand by. I'm going in."