Fever Crumb: Scrivener's Moon by Philip Reeve.

 This is the third in the series begun with Fever Crumb.  The whole series are prequels to the Sci Fi classic, Mortal Engines.  In this adventure, Fever returns to London, only to be quickly bored by the social events and engagements arranged by her Scriven mother, Wavey Godshawk.  When her mother hears of a pyramid in the North Countries that might contain the answer to Scriven history and technology, Fever jumps at the chance to accompany her on an expedition to investigate.  On the way, the group is captured by forces that intend to attack the new mobile London being built by Fever's Dad.  Fever escapes her attackers and joins some Northern nomads to continue her quest for the pyramid.  Like the other Fever Crumb books, this one has a thickly layered and complicated plot line.  I there are a lot of characters, too, mostly fairly well developed so they each have personalities and back stories. It was an exciting end to the trilogy, and I think it would have been even more interesting if I had read the Mortal Engines first, so I could understand what was being foreshadowed.  Still I had a hard time getting through it.  Half way through, Fever falls in love with a northern girl and spends a lot of time struggling with her same gender attraction.  The book suggests that the attraction is partially due to Godshawk's memories that Fever carries in her head. Still, I really didn't want to read about how much Fever wanted to kiss Cluny, and admired how the sun caught her hair etc.  If it had been a heterosexual romance, I probably would have enjoyed the book much more.  I guess I am old fashion, but reading about a same gender romance still makes me feel uncomfortable.  (341 p)