It was the Darkest of the trio; Well written, John was a very captivating character, Bartimaeus was at his best against the merc. It introduces the mercenary, Hopkins and Honorius, it's the best for me.
I think in Ptolemy's Gate how much damage the human world can do to spirits and we saw Barti at his weakest, and I think it was great to see a different side of Barti, not that it's cool when he's weak.