He went to the garden shed under the cover of darkness. He retrieved the heavy tubs of shock treatment and chlorine granules he usually used very sparingly.
Arthur began adding the granules to the water, far more than the recommended dose for regular maintenance. The pump hummed in the night, churning the mixture into a potent, invisible trap. The water clouded momentarily, then settled back into a deceptive calm.
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He slept poorly, listening to the filter working overtime. By morning, the pool looked inviting again, perhaps just a little hazy. He waited by the kitchen window, sipping coffee, his stomach in knots as he watched the house next door.