A Court of Embers and Ash by The Academy

She has been mapping the edge of the end of the world for six years. She did not expect the most dangerous man in the Shattered Meridian to be standing on the other side of it.

Mara Voss is a cartographer who works the Borderlands, charting the slow, catastrophic expansion of the Rift, a tear between worlds that has been growing since the five ruling Courts failed to stop it. She does it alone, on her own time, with her own data, because the institutions responsible for caring have stopped doing so. She is very good at it. She is also, it turns out, something the ancient records call a Riftborn, a person born with the ability to hear the Rift the way other people hear music, and that ability is the only thing that can find who is dismantling the last line of defense before the world tears open completely.

Kael Draveth, Lord of the Ember Court, made a mistake seven years ago. He has been trying to correct it ever since. He did not expect the correction to arrive in the form of a cartographer who steps on his authority the way she steps around everything else, with complete professional confidence and zero interest in being managed.

Someone has been breaking the Rift's nine anchor sites one by one, with surgical precision, for seven years. Two sites remain. The clock is running. And Mara and Kael are going to have to work together long enough to find out who, why, and whether any of this can still be stopped, which would be easier if neither of them was in significant danger of making a second, entirely different kind of mistake.

Dark fantasy romance. Slow burn. High stakes. A heroine who takes notes on everything, including things she absolutely should not be feeling. A hero who calculates twelve moves ahead and still did not see her coming.