Defy the Night by Brigid Kemmerer — book slip

In the kingdom of Kandala, a deadly plague ravages the land, with the cure—an elixir made from Moonflower petals—available only to the wealthy. Tessa Cade, an apothecary apprentice, risks her life nightly to steal these petals and distribute the elixir to the poor. Meanwhile, Prince Corrick, serving as the King's Justice, enforces harsh punishments to maintain order. When Tessa infiltrates the palace seeking revenge, she and Corrick are forced into an uneasy alliance to save the kingdom.

For fans of Holly Black and Victoria Aveyard.