Wren and Lark Noble are not just your typical teenage twins. How can they be when one of them is dead? Wren Noble was stillborn, but with her strong tie to her sister, she's still able to be somewhat apart of the living world. 
 Lark has always been an outcast. That's because she's the only one (at least one of the few) that can see / interact with her sister let alone believe she's still around. This has made her a target for bullying and makes her feel like she doesn't fit in. She would rather be dead and with her twin, but after she attempts suicide she's locked up. 
 A year after her suicide attempt, Lark is let back into school on the condition that she not cause any trouble. She plans on keeping that condition until a group of kids her age come to her for help with a ghost. As much as they don't want to get involved, Lark and Wren can't leave them to the machinations of an evil ghost. Despite their reluctance, they might just be starting to fit in a bit. 
 I honestly don't think this book would have worked without the relationship between Wren and Lark being what it is. I think if Kady Cross had decided to write them even just slightly different than what she did the book wouldn't have been as good. It might be because Lark is a bit of a difficult character. She's used to being outcast so she's developed some strong barriers to letting people in, and when they want to come in she comes across as not very nice. She's redeemed, however, due to her devotion and love of her sister Wren. Wren, strangely enough, seems to be the more vibrant and peppy one despite being dead. Her connection to the living is stronger than it should be and it's hinted at pretty good that this could be an issue popping up later; as well as Lark's too strong connection to the dead. 
 Kady Cross sure knows how to write an eerie ghost story. The ghost haunting our unsuspecting group of kids is pretty gruesome and chilling. The pace moved really well, and I liked how the mystery unfolded. The main thing I was interested in, however, is Lark and Wren's history and what it means for their present / future. Kady Cross sets us on course for where that information can take us and I look forward to it. Their connection is not unheard of, but it's certainly not common and it effects both Wren and Lark in ways they don't understand just yet. 
 Overall, I thought this was a great first book in a series. I'm excited to read more!