It all started with a bunch of gaijin--- four of them, Americans--- who were probably the worst guests in the history of ever. Hogging the common room and openly gambling, being loud and rude, expecting better service than given to the other guests. The last straw is the coffee. The gaijin demand that Shiro make coffee, when he's busy with the rest of the traditional Japanese breakfast. Shiro, being nice and obliging and having Kuro to fall back on, makes coffee. The smell wakes up everybody else, including Misao. Shiro explains why he's making coffee. Misao gets pissed, pouring some (but NOT a lot) coffee for herself and drinking it. She talks to the person who poisoned the coffee, not knowing that she's drinking poison. She chews the gaijin out and then heads back up to her room to change into her onmitsu uniform (intending to head to the dojo and train a little), encountering Aoshi along the way. She promises Aoshi that she'll head out to bring him tea sometime today, even if the Aoiya is busier Aoshi notices that she seems to be having some difficulty swallowing and that her pupils are dilating.
Two hours later, Aoshi wanders into the common room, looking for Misao. She's not there, but only one of the gaijin is still alive. The man is chugging water, but clearly having issues swallowing it. He turns to Aoshi, complains that it's too bright, sees that Aoshi has blue eyes, and begins to scream about Misao. The gaijin holds his heart and laughs, but complains of pain. He laughs until he cries, and then he dies.
A young woman, the young woman Misao talked to earlier, rushes through, with Saitoh in hot pursuit of her. He cuts her down, and she drops a little tin. Okon storms in, her shuriken drawn. She sees the tin and picks it up, opens it, and inspects the contents. "belladonna," she proclaims, and explain what it does: western women use it to widen their pupils, because that's beautiful, but it makes it a little hard to swallow for like 2 days and sometimes your heartbeat speeds up. Too much, Okon says, is poison.
Aoshi looks at the dead man, then thinks of Misao. He seems dazed, worried. The blood drains from his face as he says, "Dilated pupils. Difficulty swallowing. Increased heartrate." He's obviously thinking of somebody. He asks if Okon has seen Misao today. Okon hasn't.
Aoshi walks very quickly to the dojo. No Misao. He outright runs, practically flying up the stairs, to Misao's room. He slams open the door, and there's Misao, half-dressed, kneeling on her futon and crying, clutching her heart and throat, trying to swallow but unable to, her pupils wide. She whimpers that no matter what she does, the room is too bright, and that her throat and heart hurt.
Not sure where to go from there. Obviously, Aoshi is going to need a doctor. He may need to take her through meditation techniques to slow her heartrate, and also to ease her ability to swallow. The giddiness, the doctor says, won't go away until her pupils return to normal, and they need to keep her away from bright light.