"Beware the Physical Exam!" (身体検査にご用心"Shintai Kensa ni Go-yōjin") is the third episode in the series.
The time has come for the school's physical examination, and with them the realization that Haruhi's big secret is in danger of being discovered. Anxious not to lose their "secret princess," the Host Club boys come up with assorted outlandish plans to conceal her gender. None of them work until Kyoya steps in, explaining that the doctors performing the exams are all employed by his family's hospital network. He swears a female doctor to secrecy and establishes a separate 'boys' special clinic' where Haruhi can be examined in privacy.
Just after Haruhi departs for the clinic, a female student is overheard weeping and complaining that a doctor grabbed her shoulder and attempted to "make a pass" at her. Kyoya realizes this must be the strange figure in a lab coat he had noticed earlier. The girl then tells a security officer that the man ran off in the direction of the boys' special clinic; the six Host boys, worried for Haruhi's safety, rush after him. They arrive in time to find the strange man trying to prevent her from screaming, and immediately take steps to protect her.
The steps turn out to be unnecessary, however, as the man is Dr. Yabu (literally, "Quack Doctor") and is completely harmless. He came to the school in search of his daughter, whom he has not seen since she and her mother left him due to financial problems; rather than trying to make a pass at the female student, he was only trying to ask if she knew where he might find his daughter. Kyoya sensibly points out that, given the doctor's financial situation, his daughter would be a student at Ouran Public High School - not the prestigious and very expensive Ouran Academy. Nevertheless, Tamaki takes pity on him, and has Kyoya provide him with directions to the correct school. He acknowledges that there's no guarantee the daughter will forgive her father or want to speak to him, but Dr. Yuba needs to find out for himself.