Female teacher, until she falls... a false priest

Izumi (Hitomi), a high school teacher who is about to marry her colleague Ishihara, is almost raped by Kanzaki, the principal's son. Fearing that the incident will be discovered, the Kanzaki parents lock Izumi in the basement with the help of her twin sister Natsumi (Hitomi), who holds a grudge against Izumi.