As the wind gently swept across the rooftop, Martin's gaze locked onto the silhouette of the Mystery Agent. She stood at the edge, her back to him, her long black coat swaying with the breeze.
When she turned around, there was a faint smile on her lips as she handed him a sleek black cellphone. The brand was unfamiliar, one he had never encountered before. There were no markings or logos, just a simple design with a few features.
"This," she began, gesturing toward the phone, "is your key to the underground."
Martin examined the device in his hand. It felt heavier than it looked, solid and compact.
When he turned on the screen, there were only a few basic functions: calls, SMS, and an icon that intrigued him—a built-in app called "Underground."
