This Monster of Mine by Shalini Abeysekara

She knows the taste of death. He’ll stoke her hunger for it.
Eighteen-year-old Sarai doesn’t know why someone tried to kill her four years ago, but she does know that her case was closed without justice. Hellbent on vengeance, she returns to the scene of the crime as a Petitor, a prosecutor who can magically detect lies, and is assigned to work with Tetrarch Kadra. Ice-cold and perennially sadistic, Kadra is the most vicious of the four judges who rule the land—and the prime suspect in a string of deaths identical to Sarai’s attempted murder.

Certain of his guilt, Sarai begins a double life: solving cases with Kadra by day and plotting his ruin by night. But Kadra is charming and there’s something alluring about the wrath he wields against the city’s corruption. So when the evidence she finds embroils her in a deadly political battle, Sarai must also fight against her attraction to Kadra—because despite his growing hold on her heart, his voice matches the only memory she has of her assailant…

A dazzling Ancient Rome-inspired romantasy debut, This Monster of Mine is a bloodbath of manipulation, deception, and forbidden love.