Wilder Girls by Rory Power

Eighteen months before the novel's events, a mysterious illness known as the Tox began infecting the island. Initially affecting the teachers, the disease soon spread to the students, causing grotesque and often deadly mutations. The school has been under strict quarantine ever since, with the remaining girls awaiting a promised cure from the Navy.

The narrative centers on Hetty, who, along with her best friends Byatt and Reese, navigates the daily horrors of their transformed world. When Byatt disappears under suspicious circumstances, Hetty is determined to uncover the truth, leading her to question the reality of their confinement and the intentions of those in power.