City of Souls and Sinners by Kayla Edwards

Loren and Darien have settled back into their old routines, grateful that the whirlwind of dangers they’d faced on Kalendae are now behind them - or so they think. But Loren soon finds herself caught in a new storm when the Terran Imperator blackmails her into working for him. There’s only one problem: he expects her to use her magic, and she doesn’t seem to have any left. To keep Darien safe, she agrees. But the secrets she is forced to keep, and her involvement with the imperator’s son, threaten to drive her away from Darien in ways she might never recover from…