Davis said with impatience, seemingly directed against himself, "It's narrowed two hundred yards in the past half-hour. It must be tending toward something! There has to be a conclusion to it! Something must be about to happen!" Deirdre said slowly, "If it's the equivalent of a seine being hauled, with a hum instead of a net, what's going to happen when it's time for the fish to be boated?" Davis ignored her for a moment. Then he said irritably, "Everyone seems to have more brains than I do! Tony, break out those gun-cameras. Nick, get back and report if the bright spot's getting any smaller. I wish you weren't here, Deirdre!" The two crew-cuts moved to obey. Terry, alone, had no specific duty assigned to him on the yacht, unless tending to the recorder was it. He bent over the instrument which was playing in the air anything that a trailing microphone picked up under water. He raised the volume a trifle. He could still hear the singular noises of the agitated fish mixed in with the thin, strangely offensive humming sound. He heard small thumpings, and realized that they were the footfalls of his companions on the deck of the _Esperance_, transmitted to the water. He heard ... Tony came abovedecks with an armful of mysterious-looking objects which could not be seen quite clearly in the slanting moonlight. He put two of them down by the wheel and passed out the others. He silently left one for Terry and another for Deirdre, while Terry adjusted tone and volume on the recorder for maximum clarity. "What are those?" asked Terry. "Cameras," said Deirdre. "Mounted on rifle stocks, with flashbulbs in the reflectors. You aim, pull the trigger, and the shutter opens as the flashbulb goes off. So you get a picture of whatever you aim at, night or day." "Why ..." "There was a time when my father thought they might be useful," said Deirdre. "Then it looked like they wouldn't. Now it looks like they may." Terry was tempted to say, "Useful for what?" But Davis' vague talk of unpleasant wrong guesses which led to even less pleasant ones had already been an admission that no convincing answer could be given him. Davis came over to him. "This has me worried," he said in a frustrated tone of indecision. "We must be near the end of some process that I didn't suspect, and the conclusion of which I can't guess. I don't know what it is, and I don't know what it's for. I only know what it's tied in with." Terry said absorbedly, "Two or three times I've picked up some new kinds of sounds. You might call them mooing noises. They're very faint, as if they were far away, and there are long intervals between them. I don't think they come from the surface."