Now he had a reason to perform one final visual check.
Celeste raised herself slightly from the water.
"Why are you staring at the equipment?"
Luke didn't answer.
Instead, he walked toward the patio cabinet and retrieved a translucent plastic bottle containing a vivid blue pool-safe tracing dye provided for a controlled diagnostic check. He'd already received instructions about its intended use and had no intention of using anything harmful.
Celeste's expression changed when she saw it.
"What is that?"
Luke approached the edge.
"A tracer."
She frowned.
"For what?"
"Something in the pool that shouldn't be there."
Celeste immediately pushed herself upright.
"You are not putting chemicals in this water while I'm swimming!"
"It's a non-toxic diagnostic dye. I'm asking you to get out first."
Her eyes narrowed.
"You're trying to scare me."
Luke set the bottle on the deck and folded his arms.
"Then get out, and there won't be an argument."
For several seconds, she glared at him. Finally, she moved toward the steps and climbed out, dripping water onto the concrete. She seized a towel from a nearby chair and wrapped it around her shoulders.
"Do whatever ridiculous demonstration you've planned," she snapped. "You're only embarrassing yourself."
Luke waited until she was clear of the water.
Then he knelt on one knee beside the decorative tile border.
He opened the tracer bottle and carefully introduced the pool-safe blue liquid near a section of the wall he'd marked during the morning inspection.
At first, the dye drifted slowly through the turquoise water.
Then something strange happened.
The dark-blue stream suddenly narrowed into a twisting ribbon and moved sharply toward a submerged opening beneath the tile line.
Luke leaned closer.
Celeste stopped drying her hair.
The blue trail continued moving toward the opening, disappearing into a narrow space that shouldn't have been drawing water under the pool's normal operating conditions.
For several seconds, nobody spoke.
Then Luke looked toward Celeste.
"Interesting."
Her face had gone pale.
"Stop that."
He glanced up.
"What?"
"Stop pouring it!"
Luke closed the bottle and set it aside.
The visible tracer already in the water continued following the unexpected current.
Celeste stepped closer.
"You're going to ruin the pool!"
Luke looked toward the blue trail.
"No. I think somebody's been using the pool for something they never told me about."
Celeste's expression hardened.
"Don't you dare accuse me of anything."