I really liked the development of the relationship between Morse and Lewis in this book. There were already a few paragraphs in the earlier books but it was never that much. Here we finally get a bit more. A lot of it is shouting at the other (Morse) or secretly wishing the other in hell (Lewis) but there are also some really touching scenes where they (in private) acknowledge that they do like and care about each other.
Apart from that the puzzle was again amazing. You always get me with classical allusions and this boks uses motifs from Oedipus in a brilliant way and generally has as much red herrings as you'd expect from Dexter.