Through Ivy & Thorns. The Bloodroot Oaths, #1

She came to steal his clan's most sacred relic. She didn't plan on the blizzard. Or the man. Elara Ashwood is a trained warrior on a mission: infiltrate enemy territory, steal the sacred key that could end a generations-old feud, and return home a hero. Disguised as a traveling herbalist, she's tracked the relic to a remote hunting lodge in the frozen Wildmoor-but a winter storm traps her there with the one man who sees through her lies.
Lachlan Thornwood is scarred, solitary, and keeper of the very key Elara seeks. He recognizes her as an Ashwood spy the moment she wakes in his lodge. He should turn her over to his father. Instead, he makes her an offer: stay through the storm, play the game, try to take the key. But if she succeeds, she'll have to kill him-because he will never stop coming for her. What begins as a deadly battle of wits becomes something neither expected.
Snowed in together for weeks, their walls crack under shared grief, reluctant respect, and a physical tension that threatens to consume them both. But Elara's mission hasn't changed, Lachaln's loyalty to his clan hasn't wavered, and in these lands, the earth itself keeps score. When the grove demands they either seal their bond or pay in blood, Elara and Lachlan must decide what matters more: the war they were born into, or the love they never saw coming.