Late at night, five days after the first murder, I received a call from Xiaotao. "Song Yang, these bastards have committed another crime!" she said solemnly.

I asked for the address and took a cab there alone. The crime scene was located in the urban area–the top floor of a newly capped high-rise building. It was discovered by an old security guard on his night patrol who almost got a heart attack.

When I arrived at the scene, I was greeted by two bodies lying on the ground, a man and a woman. Upon seeing their faces, I couldn’t resist a sharp intake of breath. The victims’ faces had melted like hot wax, corroded beyond recognition!

Not only their faces, but also their fingers suffered the same treatment so no fingerprints remained.

"It doesn’t look like sulfuric acid,” Xiaotao remarked. “The corrosive effect is stronger than sulfuric acid, so...