Shen Tinglan, a chemistry PhD, transmigrates into the body of a condemned woman sentenced to exile. At the marriage-assignment ceremony, everyone scrambles to choose powerful and wealthy men, but she deliberately chooses Lu Chen, a well-digger whose body is covered in festering sores and who is destined to die within three days. By testing poison with a drop of blood and fighting poison with poison, she saves her supposedly useless husband in just three days, then forces Su Jin'er, the fake heiress, to kneel and kowtow. With a silver needle, she exposes a scam involving fake antidotes. She drinks poisonous dew before everyone at the execution stake to prove her innocence, then uncovers the sinister operation behind an underground poison den. The poisonous mist that has trapped the city for three years turns out to be part of the chief minister's rebellion, affecting thirteen cities across the country. An imperial envoy frames her as a remnant of a former dynasty's poison sect, but her supposedly useless husband turns the tables by producing the Ninth Prince's token. Before the chief minister is brought to justice, he detonates an underground poison storehouse. She uses poison to counter poison and disperses the poisonous mist engulfing the entire city.