Character Analysis
Celia is Whit's girlfriend. Or at least she was… See, three months prior to Whit and Wisty getting arrested, Celia disappeared without a trace. It turns out she was murdered by the New Order. Yikes, right? And it gets freakier: "They said it was because of you and your sister" (37.12), she tells Whit. Why? Well, that remains unclear.
The good news is that Celia is now a Half-light, which means she is still around, albeit as an insubstantial being in a purgatory-type place called the Underworld. She's able to make short trips into the Overworld, and it's during one of these jaunts that she helps Whit and Wisty break out of prison. She can't stay with them, though; if she remains in the Overworld too long, even her ghostly form will cease to exist.
Whit loves Celia, even in death, but perhaps the most powerful testament to her virtue is how much Wisty cares about her. "Celia was everything I wasn't, and secretly wanted to be," Wisty tells us. Wisty wants to use her powers to help Celia come back to her world, but Celia says that even magic can't help her now. That's a shame, because she doesn't seem to like the Underworld—and she doesn't know when, if ever, she'll get to come back to visit Whit.