The Seika Academy swim team arrives at a remote southern island for a training camp, where they are greeted by their new caretaker, Riku Omi. While settling in, Riku discovers a disturbing diary and hidden camera footage left behind by his predecessor, revealing a sinister history of blackmail and sexual abuse. As Riku uncovers the horrific ways the previous caretaker manipulated and violated the girls, specifically Yoshino, he realizes the true, dark nature of the island.
The caretaker uses compromising footage to blackmail and sexually exploit Matsuri and Yoshino, eventually coercing Nagisa and Shiori into his perverse games as well. After forcing all four girls into a group encounter, the predator's reign of terror ends when he is discovered drifting offshore and arrested by the police, leaving the girls to deal with the fallout of the scandal.