The three-headed giant demon was not foolish. They earlier obtained the secret allegiance of the Black Crane Taoist under the pretense of aiding him to prolong his life; and later, upon unexpectedly capturing the Nangong family's young mistress returning home, the three demons together hatched a venomous scheme.
Black Crane Taoist had been acquainted with the Nangong Family Head for many years and was well aware of the secret of the Nangong family's Soul Lamp. Thus, the three great demons brazenly pressured the Nangong clan while the Black Crane Taoist feigned lingering around Ling City.
As they say, major clans have no kinship; thus, it was natural to draw the Nangong family into the trap.
This maneuver, exploiting the dark side of human nature, was as seamless as antelope horns, naturally integrated, and was bound to lower the guards of all parties within Ling City to the greatest extent.