A Goodreads "YA Best Book of the Month"
An Amazon "Best Book of the Month: Science Fiction & Fantasy"

Zera is a Heartless—the immortal, ageless soldier of a witch. Bound to the witch Nightsinger, Zera longs for freedom from the woods they hide in. With her heart in a jar under Nightsinger's control, she serves the witch unquestioningly...until Nightsinger asks Zera for a prince's heart in exchange for her own.

But if Zera's discovered infiltrating the court, Nightsinger will destroy her heart, rather than see her tortured by the witch-hating nobles.

Crown Prince Lucien d'Malvane hates the royal court as much as it loves him—every tutor too afraid to correct him and every girl jockeying for a place at his handsome side. No one can challenge him—until the arrival of Lady Zera. She's inelegant, smart-mouthed, carefree, and out for his blood. The prince's honor has him quickly aiming for her throat.

Now it’s a game of cat and mouse between a girl with nothing to lose and a boy who has it all.

Winner takes the loser's heart.

Literally.

The Bring Me Their Hearts series is best enjoyed in order.
Reading Order:
Book #1 Bring Me Their Hearts
Book #2 Find Me Their Bones
Book #3 Send Me Their Souls