The sound of water dripping echoed from deep inside the cave. It wasn’t random. It was too steady like a clock ticking. Leah felt it right away. Something was wrong.

She grabbed Jason’s arm and pulled him back.

“That’s not water,” she whispered. “It could be a timer. Or a sensor. Something dangerous.”

Jason held his mother’s locket tightly in his hand. He felt a cold fear in his chest. The locket left here at David’s old secret place wasn’t a coincidence. It had to be a warning. Or a message.

“What kind of timer?” Jason asked quietly.

“It could be anything,” Leah said, scanning the ground, the cave walls,...