The Third Daughter is a sapphic, dual POV fantasy that blends the complex family politics of Kendare Blake's Three Dark Crowns and the sweeping lore of Marie Rutkoski's The Midnight Lie in an examination of power, the roles we are born into, and the impact of our emotions. For centuries, the country of Velle has waited for their highest deity, the New Maiden, to return. The prophecy tells not when, but how she will appear: as the third daughter of a third daughter.

When the fabled child is finally born to Velle's reigning queen, the only citizen who does not rejoice is Elodie: the queen's eldest daughter who has lost her claim to the crown. When her mother unexpectedly passes and her young sister takes the throne, Elodie's future in Velle is threatened by a vindictive chaplain and a church wielding ultimate power. The only way to preserve her mother's legacy is to retake the throne.

To do so, she must eliminate the Third Daughter - her own sister. Desperate, Elodie slips away to the Midnight Market to purchase poison from an apothecary. Instead, she finds Sabine.

Sabine sells sadness. Just a single tear added to one of her mother's potions enhances the brew tenfold. But Sabine mistakenly sends Elodie away not with the poison she requests, but with a vial of her tears.

Sabine's sadness does not kill the young queen. Instead, the maiden slips into a slumber from which she will not wake. As the church hunts down the person responsible for the Third Daughter's condition, Sabine and Elodie must work together to find a way to wake her before Elodie's siblings learn the truth and Sabine loses her magic - and herself - to the darkness that threatens to consume her.