It was shortly after midnight when a persistent nightmare aroused Don Foster from sleep. For a moment he lay drowsily in his blankets there on the sand, with memory of the nightmare still vivid. It had been a monstrous flying thing like a giant blue-bottle fly that he had been battling in his sleep. Memory of the thing's high-pitched, droning buzz still rang in his ears. Then abruptly he realized that the peculiar buzzing was no mere echo of a nightmare. It was an actual sound that still vibrate