In the first year of Emperor Renzong's Jiayou era, rumors spread throughout the capital of Dongjing about a hat-shaped monster capable of flying through the sky and burrowing underground. At night, it would invade commoners' homes to harm people, showing a particular preference for devouring women and young children. This caused widespread panic and unrest both inside and outside the imperial court. Consequently, Emperor Renzong ordered Bao Zheng, who had been exiled to the countryside, to return to the capital immediately and thoroughly investigate the case.