Mercer froze, fingers hovering just above the clasp. He glanced around. The train car remained unchanged—faces down, lost in thought. But the warning echoed, as real as the briefcase before him. He swallowed, drew his hand back. The lights steadied. The train’s clatter filled the silence. He watched the briefcase. Waited. Nothing happened. Except—a faint tap, from inside the case. Once. Then silence. Mercer stared, breath held. He was no longer sure if he wanted to know what came next.