The Assassin and the Pirate Lord by Sarah J. Maas

Celaena Sardothien, dispatched by the Assassin’s Guild, finds herself on a secluded tropical island in the midst of a vast sea. Her purpose: to claim a debt owed by the notorious Lord of the Pirates. However, when Celaena discovers that the payment entails human lives instead of currency, her mission takes an unexpected turn. Driven by her unwavering sense of justice, she embarks on a perilous journey, willing to sacrifice everything to rectify the injustice she was initially assigned to enforce.