Court of Night by C.N. Crawford — book slip

As a Knight of the Shadow Fae, Arianna is tasked with defending the Institute against dark magic, death cults, and demon roller discos.

Her new life begins with an impossible choice: turn over Ruadan within twenty-four hours, or face the unleashing of the Black Death.

Meanwhile, her old gladiator master threatens to reveal her identity, putting her position at the Institute at risk.

If Arianna can't find and kill her oldest enemy in time, the Black Death will be unleashed, and she'll be on the run once more.