Grave Mercy by Robin LaFevers
The daughter of Death is determined to serve him...no matter what happens.
The year is 1485, and young Ismae is rescued from a potentially brutal marriage by a local hedgewitch, who recognizes the terrible scars on the girl's back as a mark of her true parentage: her father is Mortain, the god of death. Spirited away across Brittany, Ismae ends up at the convent of Saint Mortain, where she is instructed by nuns in the skills needed to serve their god: poisoning, fighting with swords, knives and crossbows, as well as the miscellaneous useful skills for assassins and spies, tactfully referred to as the "womanly arts."
Leaving the convent for the first time as a trained killer, Ismae's assignment is to journey in the disguise of "cousin" (mistress) with handsome Gavriel Duval to the castle of the young Dutchess of Brittany, and kill whoever needs to be killed in order to protect and support the dutchess. Sometimes the killing is quick and ruthless; occasionally, it is an act of kindness. But when the order comes for Ismae to kill Duval, she looks beyond her convent education for answers.
An engaging narrative voice and colorful world-building turn a predictable plot into an exciting tale of romance and intrigue. The book is first in a trilogy, but stands alone well. No cussing and limited gore; contains violence and references to lusty situations, but the sex occurs off-page and late in the book. References to "old gods" masquerading as "modern saints" may bother some readers.
Recommended for readers ages 14 to adult who enjoy historical and supernatural romances with strong female characters.