The night Lyssa Cadogan's brother was murdered by a faerie-made monster known as the Beast, she made him a promise: she would find a way to destroy the immortal creature and avenge his death. For thirteen years, she has been hunting faeries and the abominations they created. But in all that time, the one Beast she is most desperate to find has never resurfaced.

Until she meets Alderic Casimir de Laurent, a melodramatic dandy with a coin purse bigger than his brain. Somehow, he has found the monster’s lair, and—even more surprising—retrieved one of its claws. A claw Lyssa needs in order to forge a sword that can kill the Beast.

Alderic is ill-equipped for a hunt and almost guaranteed to get himself killed. But as the two of them search for the rest of the materials that will be the Beast's undoing, Alderic reveals hidden depths: dark secrets that he guards as carefully as Lyssa guards hers. Before long, and against Lyssa's better judgment, an unlikely friendship begins to bloom—one that will either lead to the culmination of Lyssa's quest for vengeance, or spell doom for them both.