I really like it when stories use the plot element of an unscrupulous character (in this case, a gang leader buying the antidote and selling it to the city and ending the current plague) inadvertently doing good. Like in Shield Hero where the slaver sells Raphtalia to Naofumi and inadvertently gives her a chance at a much better life and a chance to become stronger and save her people while also helping naofumi regain his humanity and save the world. This trope is good writing.