This homage to A TALE OF TWO CITIES (which I've never read) was Brennan at her best. She shines brightest with her snarky dialogue, but that doesn't mean that her world-building and characters aren't also excellent.

Lucie grew up in The Dark, and has rescued her poor father, taking him to The Light. She falls in love with Ethan, who just so happens to be the son of the most powerful man in The Light City and a thoroughly decent guy. Lucie has to make peace with what she had to do to escape and survive, as well as decide what sort of person she wants to be.

There's magic, doppelgangers, loyalties forged and broken, and it's a romping good ride. Full of heartfelt emotion, loss, and hope, Brennan breaks your heart as only she can.