Hazel and Frank's relationship kind of weirded me out (13yr old and 16yr old) but don't let it discourage you from reading the book, much better than The Lost Hero (first book in the series)  in my opinion,  because unlike The Lost Hero I found the plot and characters more interesting. Plus there were more characters and references from the Percy Jackson series in it which I enjoyed a lot. Do wish more of the relationships in the series were more slow burn (like how Percy and Annabeth's getting together was built up over 5 books) because I feel like both times (The Lost Hero and this) it was done too quickly for me to really care about them getting together.