The plot and the world were great, original and the best aspect of the book. I loved it. The characters, however, were...not good. None of them felt real at all. None of them made that leap from the pages of the book that so many good characters make. I felt no particular attachment to any of them, and the only thing that made me care if the author suddenly decided for them all to just sink through the ground to the center of the Earth was that it would screw with the plot. I didn't like Mary from the start and my dislike just grew from there, especially toward the end. I could never take the McGill seriously. Allie and Nick were the best of the bunch, though that isn't saying much. The rest of the characters were forgetable. 
 What this book lacks in the character department, however, it makes up for somewhat in the world and plot. I liked it a lot. This book would've been five stars if I didn't have to take the characters into consideration. 
 If you wanna read a book with a great story, read this. But if you're looking in the pages for friends to hold near to your heart, look somewhere else.