This fourth installment of the Heroes of Olympus Series starts right in the middle of the action from where the last book left off. I have enjoyed this series tremendously and I think that Rick Riordan really got to know his characters with this book. 
 From the struggles of Percy and Annabeth in Hades to the inner demons each of the other Olympians has to deal with as the progress towards their destined event, the depth and variety of voices in each of the chapters in this children's book is fantastic. 
 I couldn't help but feel that I was reading a compilation of several short stories as I read through this novel. Perhaps Annabeth and Percy's struggle was the most exciting adventure throughout as it really pushed my imagination with visions of Hades and it developed what it means to be in a relationship as we see Percy and Annabeth grow through their many life or death struggles. 
 A truly surprising moment of depth in this book was Jason's attempt at helping Nico deal with his sexuality. Nico's revelation was kind of left field, but I think that when it comes to sexuality, its something personal that most people will only see when the person in question chooses to reveal it about themselves and I thought it was handled beautifully. 
 Leo's adventures on the island and his blossoming love with the Calypso was probably one of the most endearing segments of the book. Not only was it funny, but so very sweet that you can't help but to cheer for their success. 
 Their story along with all the others is left open ended as the series moves into its last book. Along with the emotional depth of this book, Rick Riordan does not fail to impress me with his creative approach to both Greek and Roman mythology and adding that modern day spin his series is known for. This book was an excellent follow through to Mark of Athena.