Luo Jin'an was going to the capital because of the plague, and Su Binglan thought her prescription might work since Baili Jinghua came from there.
Baili Jinghua's sickness was related to the plague, so Su Binglan figured her prescription could cure those people. Nonetheless, it was better to be over-prepared than under-prepared.
Su Binglan did not ask why there was a plague in the capital and why Luo Jin'an wanted to go because she respected him. Su Binglan would only help her husband prepare whatever he needed for his journey.
Luo Jin'an looked down at the prescription under the moonlight, and his expression changed slightly. "Do you know about the situation in the capital?"
Su Binglan explained, "Jinghua came from there and fell ill just outside of Hundred Herb Hospital, so I gave her a checkup. She showed signs of the plague at that time. Honestly, it was more like she had gotten poisoned.