That is Home - S1.E12

In an attempt to save the captive Butterfly Slaves, Ling Chang Feng enters the prison cell to assess the condition of the slaves who were fed the black peonies soup. At that very moment, black peony petals drift throughout the city, and when inhaled by the imprisoned slaves, they become restless and eventually turn to ashes. Tang Qian Yue, at this moment, also exhibits peculiar symptoms.