Cinderella's Crimes: Once Upon a Heist (Deadly Ever After) by Kelsey Josund

For years, Cinna has been forced to serve her wealthy cousins rather than attend society events alongside them. She has waited for the chance to prove herself and exact revenge. When a ball at the castle is announced, promising to bring many powerful people to town, she seizes the opportunity to strike. She bets her best friend, Johann, a small-time thief and con-man, that she can land a greater score the night of the ball than he can. They embark on parallel heists. But as their plots unfold, things begin to unravel: by the end of the night, the castle’s on lock down, a duchess is dead, a mansion has burnt to the ground – and Cinna hasn’t even stolen anything. Or has she captured something far more valuable than gold and jewels?