The old man whispered to Trevor. "I'm about to take your hand. Just follow where I lead. Do you understand?"
"I...uh..."
"We'll talk later. Do you understand? Yes or no?"
"Yes."
"Gramps attached a device no bigger than a dime to the back of Trevor's hand. "We're about to turn invisible," he said. "Are you ready?"
"Uh...Uh..."
"Say 'Bye'," Gramps said, at which point he, indeed, turned invisible.