these thinned out, so did radio reception. Camille Burkett's next broadcast came through very poorly.

There was enough in it, however, to seize the attention of the two men in the tractor.

She was saying: "—real all right, and dangerous. It's the ... thing I ever saw ... kinds of lava from what looks like ... same vent. There's high viscosity stuff building a spatter cone to end all spatter cones, and some very thin fluid from somewhere at the bottom. The flow has already blocked the valley used by the Brightside routes and is coming along it. A new return route will have to be found for the tractors that ... was spreading fast when I saw it. I can't tell how much will come. But unless it stops there's nothing at all to keep the flow away from the ship. It isn't coming fast, but it's coming. I'd advise all tractors to turn back. Captain Rowson reminds me that only one takeoff is possible. If we leave this site, we're committed to leaving Mercury. Arnie and Ren, do you hear me?"

Zaino responded at once. "We got most of it, Doctor. Do you really think the ship is in danger?"

"I don't know. I can only say that if this flow continues the ship will have to leave, because this area will sooner or later be covered. I can't guess how likely ... check further to get some sort of estimate. It's different from any Earthly lava source—maybe you heard—should try to get Eileen and Eric back, too. I can't raise them. I suppose they're well out from under the ion layer by now. Maybe you're close enough to them to catch them with diffracted waves. Try, anyway. Whether you can raise them or not you'd better start back yourself."

Hargedon cut in at this point. "What does Dr. Mardikian say about that? We still have most of the seismometers on this route to visit."

"I think Captain Rowson has the deciding word here, but if it helps your decision Dr. Mardikian has already started back. He hasn't finished his route, either. So hop back here, Ren. And Arnie, put that technical skill you haven't had to use yet to work raising Eileen and Eric."

"What I can do, I will," replied Zaino, "but you'd better tape a recall message and keep it going out on. Let's see—band F."

"All right. I'll be ready to check the volcano as soon as you get back. How long?"

"Seven hours—maybe six and a half," replied Hargedon. "We have to be careful."

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