It was fast-paced, going to the mausoleum of halicarnassus to get the next Loculus, it was kindda hectic, made a pretty big pothole, and an ugly stereotype of dwarf people.
Plothole: this is going to be a spoiler:
Jack and friends had to cross the river of nostalgiclos (or lethe in greek but nostalgiclos was a made up name) in the realm of Bo'gloo in other to meet the ruler Queen Artemisia. It is said when one cross the river they must face their greatest fear and give in rather than fight and deny it. So the fears won't consume them whole and they could passed the last 'trial' of a pure heart to meet this Queeny. Aly, Cass, and the professor bhegad did it and they got through. Jack didn't and he still got through with the help of his friends and the chaotic memory of Cass's. Cass's greatest fear was griffin and it came alive again from the river. I was hoping their fear was more deeper than that, and since Cass had a pretty bad memories of abandonment, why not use that?? Jack's greatest fear was his mom's death, which is of course more make sense. And then by facing the fear, they had lost their abilities. Which is just not great. Accept Jack of course. At the forest(?) i forgot, near the palace of the Queeny, the fire started to burst and it spread fast. They had to run, and of course the fire happened because Jack didn't face his fear. After some running and found a new portal to London, the ex-sybil, their guide, prompted them to move on to meet the queen. And she helped them go through. I mean, she's the one who mentioned all those trials and acted as a i-dont-give-a-damn villain, which is quite good, but if she's going to help them anyway, why not do it in the first place?? Makes no sense.
One thing I see a difference here is the many involvement of adults. Where usually, a middle grade adventures book like this always disregarded adult's interference. So that's quite good I guess.
Oh, and what's up with Jack passing out and woke up with a one-liner remarks from his friends. It happened too often in every books so far. Lol.