"Hold it!" I grabbed Foster's arm and pointed overhead. "What's that?"
Foster looked up. A brilliant point of blue light, brighter than a star, grew perceptibly as we watched.
"Maybe we won't get to notify anybody after all," I said. "I think that's our bomb—coming home to roost."
"That's illogical," Foster said. "The installation would hardly be arranged merely to destroy itself in so complex a manner."
"Let's get out of here," I yelled.
"It's approaching us very rapidly," Foster said. "The distance we could run in the next few minutes would be trivial by comparison with the killing radius of a modern bomb. We'll be safer sheltered in the cleft than on the open."
"We could slide down the tunnel," I said.
"And be buried?"
"You're right; I'd rather fry on the surface."
We crouched, watching the blue glare directly overhead, growing larger, brighter. I could see Foster's face by its light now.