Nervously alert, strung to extreme tension, but without alarm, still playing at the game of tracking, Jerry followed.
From the pool came occasional cries and laughter, and each time they reached his ears Jerry experienced glad little thrills.

Had he been asked, and had he been able to express the sensations of emotion in terms of thought, he would have said that the sweetest sound in the world was any sound of Villa Kennan's voice, and that, next sweetest, was any sound of Harley Kennan's voice.

Their voices thrilled him, always, reminding him of his love for them and that he was beloved of them.
With the first sight of the strange black, which occurred close to the pool, Jerry's suspicions were aroused.

He was not conducting himself as an ordinary black, not on evil intent, should conduct himself.

Instead, he betrayed all the actions of one who lurked in the perpetration of harm.