4.5 stars. Excellent. I really enjoyed this. The mystery was quite interesting, although not too difficult to work out. Although you are never quite sure until near the end.
The tentatively developing relationship between Adrien and Riordan is also nice. Although nothing happens between them, there is an obvious attachment/affection growing. It will be interesting to see where this goes in the next book.
The only thing I wasn't so keen on is that I felt it ended slightly abruptly for me and I felt that the actions of Adrien at the end were a bit stupid. Otherwise I think I would have given this 5 stars.