Echo in Onyx.
(Book)

A Murder and a Masquerade: Brianna loves her new job as maid to Lady Marguerite. Like many high nobles, Marguerite is attended by echoes, silent creatures who look exactly like her and move in perfect synchronicity. News soon comes that Marguerite has been invited to the royal city as a potential bride for the crown prince. Brianna is delighted to accompany Marguerite to the city—and perhaps get a chance to continue her own flirtation with Nico, one of the king’s inquisitors. Then, disaster strikes on the road when they come under attack. The brutal assault forces Marguerite and Brianna to concoct a desperate plan. Their subterfuge just might work—but only if Brianna can keep Nico from learning the truth. And only if Marguerite can give up her own secret, doomed romance. And all that’s at stake—is the very future of the kingdom.