This was a really good sequel, that i really enjoyed. Its all about Nikki trying to find Jack who was taken by the tunnels in the last one when he sacrificed himself for her. Nikki is desperate for a way and needs Cole's help in order to reach Jack. 
 Most of the book takes place in the Everneath, and i found learning about it and seeing their world in more detail really cool. It was quite different to how i expected and i hope we get to delve more into it and their mythology in the next one. 
 Jack is absent for most of the book, but it doesn't feel that way, as there are lots of flashbacks, and various memories of Jack and Nikki that we get to read about. Its also good as we get to see the start of their romance and their first kiss and stuff that i always love reading about. 
 I liked Cole in this book; we get to see a different - sweeter and caring side of him. I even felt a little sorry for him at some points but he really annoyed me at the end. I wish he hadnt done what he did as thats just gonna make Nikki hate him. Despite all this, i still prefer him to Jack as i just find him more interesting and hope he gets a proper shot with her. 
 The cliffhanger is MASSIVE! It ends with a GIGANTIC twist that i didnt see coming a mile away. I m sure it will make things really interesting in the sequel and i cant wait to read it.